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HUMAN PSYCHOLOGY 



BY 

HOWARD C. WARREN 

Stuart Professor of Psychology 
Princeton University 



3X. 



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HOUGHTON MIFFLIN COMPANY 

BOSTON NEW YORK CHICAGO 



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COPYRIGHT, I9I9, BY HOWARD C. WARRBN 



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CAMBRIDGE • MASSACHUSETTS 
U • S • A 



CONTENTS 

lAPTEB PAGE 

I. The Science of Psychology 1 

Preliminary Definitions, 1. ^^ 

Science, 1. <>^ 

Classification of Science, 3. 
Organisms and Organization, 6. 
Vital Life and Mental Life, 7. 
Self-Observation; Consciousness, 9. 
Behavior and Conscious Experience, 10. 
'Definition of Psychology, 13. ^^ 

"Chief Branches of Psychology, \Z. ^ .u^ 
Reading and Exercises, 16. 

II. The Organism 17 

Vital Organization, 17. 

Classes of Vital Functions, 22. 
Mental Organization, 24. 

Classes of Mental Functions, 26. 
Evolution of Mental Life in Organisms, 28. 
Mental Life as Psychobiological Organization, 28. 
Summary of Chapters I and II, 29. j^^ 

Reading and Exercises, 30. 

in. The Neuro-Terminal Mechanism . ... 32 

Structural Basis of Mental Life, 32. 
Nervous System : Structure of the Neuron, 34. 

Cerebrospinal System: General Plan, 38. 

The Spinal Cord, 43. 

The Brain, 44. 
The Cortex, 46. 

Autonomic System, 49. 
Terminal Organs, 51. 

1. Receptors, 51. 

2. Effectors: Muscles and Glands, 52. 

Reading and Exercises, 55 



vi HUMAN PSYCHOLOGY 

CHAPTER PAGE 

IV. Physiology of the Neuron 56 

Functional View of the Nervous System, 56. 
The Nerve Impulse: Intensity and Mode, 56. 
Fundamental Operations of Nerve Substance, 59. 

1. Excitation, 60. 

2. Conduction, 61. 

3. Retention, 63. 

4. Metabolic Variation, 66. 

5. Summation of Impulses, 67. 

6. Distribution of Impulses, 68. 

7. Modification of Impulses, 69. 
Summary of Nerve Physiology, 70. 

Reading and Exercises, 71. 

V. Stimulation, Adjustment, and Response . . 72 

The Nervous Arc and its Segments, 72. 
Operation of Each Segment. 73. 

1. Stimulation, 74. 

Nature of Stimulation, 74. 
Role of the Stimulus, 75. 
Role of the Receptor, 78. ^ 
Role of the Sensory Neurons, 80. 
General Laws of Stimulation, 80. 

2. Response, 81. 

Nature of Response, 81. 

a. Muscular Response, 81. 
• Mode of Impulse, 82. 

Other Factors determining Response, 83. 

b. Glandular Response, 84. 
General Laws of Response, 84. 

3. Adjustment (Integration and Coordination), 85. 

Nature of Adjustment, 85. 

R61e of Retention and Modification, 86. ' 

Role of Metabolic Condition, 87. 
Laws of Adjustment, 88. 
Significance of the Central System, 88. ■ 
Methods of Investigating Adjustment, 89. 
Reading and Exercises, 91, 



/ 



CONTENTS vii 

CHAPTER PAGE 

VI. Behavior 92 

Operation of the Nervous Arc; Adaptive Reaction, 92. 
Concept of Behavior, 94. 
Types of Behavior, 94. 

1. Reflex Behavior, 95. 

Reflex Action, 95. 

Simple Reflexes, 96. 

Compound Reflexes, 97. 
Nature of the Reflex, 99. 
Human Reflexes, 100. 

2. Instinctive Behavior, 102. 

Relation of Instinct to the Reflex, 102. 
Evolution of Instinct, 103. 
Classes of Hiunan Instincts, 104. 
Instinctive Tendencies, 107. 
Development and Variability of Instincts, 109. 
Reading and Exercises, 111. 

VII. Behavior (continued) , . 112 

3. Intelligent Behavior, 112. 

Nature and Neural Basis of Intelligence, 112. 
Intelligence and Habit, 115. 
The Learning Process, 116. 

a. Acquisition, 117. b. Fixation, 120. 
Adaptation to New Situations, 124. 
Growth of Intelligence, 126. 
Significance of Intelligence, 128. 
Summary of Chapters V to VII, 131. 

Reading and Exercises, 132. 

VIII. Conscious Experience . . . . . . 133 

The Method of Self-Observation and its Data, 133. 
Casual and Scientific Self-Observation, 134. 
Characters of Experience: Quality and Intensity, 137. 
Fundamental Operations of Experience, 138. 

1. Impression, 138. 

2. Suggestion (Successive Association), 138. 

3. Revival (Memory), 140. 

4. Vividness (Attention, Focalization), 140 

5. Combination (Simultaneous Association), 142. 



viii HUMAN PSYCHOLOGY 

CHAPTER PAGE 

6. Discrimination, 143. 

7. Transformation ('Mental Chemistry'), 143. 
Subconscious Experience, 144. 

Marginal Consciousness, 146. 
Hyperesthesia and Anesthesia, 147. 

Fundamental Types of Experience: Sensation and Ideation, 147. 
Summary of Conscious Experience, 149. 
Reading and Exercises, 150. 

IX. The Senses 151 

1. Sight (Vision), 151. 

Structure of the Eye, 151. 
Physiology of the Eye, 157. 

Ciliary and Iris Reflexes, 158. 

Eye Movements, 160. 
Visual Stimuli, 160. 
Characters of Visual Sensation : Qualities, 163, 

a. The Color Series; Hues, 163. 

b. The Gray Series; Shades, 167. 

c. Mixed Series : Color-Shades and Tints, 168, 
Number of Qualities; Color Spindle, 170. 
Purkinje Phenomenon; Adaptation, 173. 
Complementaries, 174. 
After-Sensations, 175. 

Contrast, 176. 
Peripheral Vision, 176. 
Color Blindness, 177. 
Theory of Visual Qualities, 180. 
Visual Intensity, 181. 

Reading and Exercises, 183. 

X. The Senses {continued) 184 

2. Hearing (Audition), 184. 

Structure of the Ear, 184. 

Auditory Stimuli, 188. 

Physiology of Hearing, 190. 

Characters of Auditory Sensation: Qualities, 191. 

Tones (Pitch), 191. 

Overtones and Timbre, 194. 

Combination Tones and Compound Clangs, 194. 
Intensity, 196. 



CONTENTS ix 

CHAPTER PAGE 

3. Smell (Olfaction), 196. 

Structure of the Olfactory Receptor, 196. 
Olfactory Stimuli and Physiology of Smell, 197. 
Sense Characters: Qualities, 197. Intensity, 198. 

4. Taste (Gustation), 199. 

Gustatory Receptor and Stimuli, 199. 
Characters of Gustatory Sensation, 200. 
5-7. Cutaneous Senses: Touch, Warmth, Cold, 201. 
Receptors for Cutaneous Sensibility, 201 . 
Qualities and Intensity of Cutaneous Sensations, 203. 

8. Organic Senses (Ccenesthesia, Visceral Senses), 204. 

Classes of Systemic Sensations, 204. 
Qualities of Organic Sensations, 205. 

9. Pain Sense, 207. 

Pain Stimuli and Qualities of Sensation, 207. 

10. Kinesthetic Senses (Muscle Sense), 209. 
'^ Classes of Motor Sensations, 209. 

Kinesthetic Stimuli and Sensations, 209. 
Kinesthetic Qualities and Intensity, 210. 

11. Static Sense, 211. 

Static Receptor and Stimuli, 211. 
Reading and Exercises, 214. 

XI. The Components of Mental States . . . 215 

Mental States and their Components, 215. 

1. Sensations, 216. 

Characters of Sensation, 216. 
Role of the Stimulus, 217. 
Role of the Receptor, 218. 

Defective Receptors, 220. 
Classes of Sensations, 221. 

External, Systemic, and Motor Senses, 222. 
Number of Different Sensations, 223. 
Summary of Sensation, 224. 

2. Ideas, 225. 

The Ideation Process, 225. 
Role of Ideas in Mental Life, 227. 
Distinction between Ideas and Sensations, 228. 
Border-line Experiences, 229. 
Classes of Mental States, 230. 

Reading and Exercises, 232. 



X HUMAN PSYCHOLOGY 

CHAPTER PAGE 

XII. Primary Mental States ...... 233 

1. Perceptions, 233. 

Nature of Perception, 233. 

a. Simple Perception, 234. 

b. Surface Perception, 235. 

Central Mechanism, 239. 

c. Depth Perception and Projection: Visual, 241. 

(1) Uniocular Factors, 241. 

(2) Binocular Factors, 244. 

Central Processes in Visual Projection, 246. 
Projection in Other Senses, 247. 

d. Apperception (Focused Perception), 249. 

e. Object Perception, 251. 

f. Perception of Time, Rhythm, and Events, 255. 

g. Perception of Differences (Discrimination), 257. 
Truth and Illusion in Perception, 258. 

Relation of Perception to Sensation, 266. 
Physiology of Perception, 267. 
Reading and Exercises, 268, 

XIII. Primary Mental States (continued) . . .. 270 

2. Imagery, 270. 

Nature and Classes of Imagery, 270. 

a. Memory Images, 271. 

b. Free Images, 274. 

c. Anticipation Images, 275, 

d. Imagination Images (Fancy), 275. 

e. General Images, 276. 
Physiology of the Image, 277. 

Role of Imagery in Mental Life, 278. 

3. Feelings, 279. 

Nature of Feeling, 279. 

Characters of Feeling, 281. 

Appetite and Aversion; Excitement, 284. 

Role of Feeling in Mental Life, 285. • 

4. Conations (Expressive States), 286. 

Nature of Conative States, 286. 
Conation and Volition, 287. 
Composition of Conative States, 289. 
Varieties and Role of Conation, 290. 
Reading and Exercises, 292. 



CONTENTS 3d 

CHAPTEB PAGE 

XIV. Secondary Mental States 293 

Nature and Classification of Secondary States, 293. 

1. Emotions, 294. 

Nature of Emotion, 294. 
Primitive Types of Emotion, 296. 
Classification of Human Emotions, 298. 
Role of Emotion in Mental Life, 300. 

2. Sentiments, 302. 

Nature and Classes of Sentiment, 302. 
, Types of Sentiment, 303. 
Role in Mental Life, 305. 

3. Volitions, 306. 

Nature of Volition, 306. 
Voluntary Activity, 308. 
Purposive Factor in Volition, 310. 
Voluntary Control; Role of Volition, 311. 
Reading and Exercises, 313. 

XV. Secondary Mental States (continued) . . 314 

4. Thought and Language, 314. 

Distinctive Features, 314. 

Symbolic Character, 314. 

Social Origin, 316. 

Mutual Dependence, 317. 
Types of Language, 317. 

Comprehension and Reading, 320. 
Nature and Types of Thought, 321. 

Imageless Thought, 322. 

Meanings and Values, 323. 

Rational Thought : Concepts and Judgments, 326. 
R61e of Thought and Language in Mental Life, 328. 

5. Ideals and Rational Actions, 329. 

Their Nature and Classification, 329. 
Summary of Mental States, 331. 

Reading and Exercises, 333. 

XVI. Succession of Mental States . » . . 334 

The Stream of Conscious Experiences, 334. 
Stream of Perception, 335. 

Laws of Perceptual Succession, 337. 



xii HUMAN PSYCHOLOGY 

CHAPTER PAGE 

Stream of Thought, 338. 

Laws of Ideational Succession, 338. 

Classes of Associations, 342. 

Control and Limitations of the Thought Series, 342. 

Sleep and Dreams, 344. 

Hypnosis and Hypnotic Suggestion, 349. 
Reasoning, 350. 
General Stream of Experiences, 354. 

Reaction Time, 356. 

Laws of the Succession of Experiences, 357. 
Reading and Exercises, 358. 

XVII. Attitudes 360 

Permanent Mental^ Conditions, 360. 

1. Attitudes, 361. 

Nature and Classes of Attitudes, 361. 

a. Interest, 362. 

b. Desire, 363. 

c. Attention, 364. 

d. Dispositions, 365. 

e. Other Secondary Attitudes, 369. 

Reading and Exercises, 373. 

XVIII. Character and Personality .... 374 

2. Character, 374. 

Nature of Character, 374. 

a. Temperament, 375. 

b. Intellectuality, 376. 

c. Skill, 379. 

d. Morality, 381. 

3. Personality, 383. 

The Self, 383. 

Personal Identity and Multiple Personality, 385. 
Self-Consciousness, 387. 
Summary of Chapters XVI to XVIII, 388. 
Reading and Exercises, 389. 

XIX. Organized Mental Life 391 

Mental Development, 391. 
1. Differentiation, 392. 



CONTENTS xiii 

2. Mental Organization, 392. 

Factors which Determine Mental Organization, 394. 
Heredity and Environment, 399. 
Types of Mental Organization, 400. 
3. Control, 401. 

Personal Control and Personality, 404. 
General Summary of the Book, 405. 
Special Conclusions, 409. 

Reading and Exercises, 411. 

Appendix 

PROBLEM , PAGE 

I. The Mind-Body Relation 413 

Subjective and Objective Phenomena, 413. 
Perception of the External World, 416. 
Thought-Transference; Psychical Research, 418. 
Personal Immortality, 422. 
References, 423. 

II. Mechanism and Purpose 425 

Purpose in Organic Growth, 425. 
Conscious Purpose, 427. 

Free- Will, Determinism, and Responsibility, 431. 
Personification of Natural Phenomena, 433. 
References, 434. 

III. Neural Activity 435 

Nature and Modal Variation of the Nerve Impulse, 435. 
Retention, Metabolism, and Modification, 437. 
References, 440. 

IV. The Visual Process 441 

Principal Facts, 441. 
Three-Color Theories, 441. 
Metabolic Theories, 443. 
Genetic Theory, 445. 
References, 446. 

Directions for Performing the Exercises . . . 447 
Index 451 



ILLUSTRATIONS 

FIGURE CHAPTER PAGE 

1. The Cell and its Parts II 18 

2. Types of Cells " 19 

3. Neuro-Terminal Circuits Ill 33 

4. The Neuron and its Parts " 34 

5. Types of Neurons " 36 

6. Synapses " 37 

7. Synapses " 37 

8. Central Cerebrospinal System " 39 

9. Cerebrospinal System and Sympathetic Ganglia . . " 40 

10. Paths in Cord and Brain " 42 

11. Cross-Section of Cord " 44 

12. Model of Human Brain facing " 44 

13. Base of Brain " " 44 

14. Cross-Section of Brain " " 45 

15. Cortex, from Above " " 46 

16. Cortex, from Left Side " " 47 

17. Projection Areas in Cortex " 48 

18. Association Fibers in Cortex " 49 

19. Autonomic System " 50 

20. Muscle, with Nerve Endings " 53 

21. Alternative Nerve Paths IV 67 

22. Summation of Nerve Impulses " 68 

23. Distribution of the Nerve Impulse " 68 

24. Simple Reflex VI 96 

25. Distributed Reflex . " 97 

26. Chain Reflex " 99 

27. Mazes for Investigating Habit Formation .... VII 113 

28. Changes of Path in Habit Formation . . . . . " 118 

29. Curve of Learning " 124 

30. Cross-Section of Eye IX 152 

31. Layers of the Retina " 153 

32. Map of Blind Spot " 155 

33. Eyeball and Muscles " 156 

34. Focusing of Objects on Retina " 157 

35. Course of Optic Nerve " 159 

36. Refraction of Light " 162 



xvi HUMAN PSYCHOLOGY 

FIGURE CHAPTER PAGE 

37. Color Mixer IX 164 

38. Variations in Color-Shade and Tint " 169 

39. Color Spindle and Color Belt " 171 

40. Perimeter " 177 

41. Color Zones of Retina . " 178 

42. Masson Disk " 182 

43. Cross-Section of Ear X 184 

44. Diagram of Middle Ear ......... " 185 

45. Labyrinth and Section through Cochlea .... " 187 

46. Organ of Corti " 188 

47. Musical Intervals " 193 

48. Nasal Cavity and Olfactory Region . . facing " 196 

49. Olfactory Cells . " " 196 

50. Olfactometer " 198 

51. Tongue, showing Papillae facing " 199 

52. Taste Bulbs and Taste Cells " 199 

53. Pressure and Temperature Spots " 201 

54. Types of Cutaneous Receptors " 202 

55. Semicircular Canals " 212 

56. Space Perception in Touch XII 236 

57. Visual Space Perception " 237 

58. Curve of Weber's Law " 259 

59. A Study in Perspective .....,.." 260 

60. Staircase Illusion " 261 

61. Illusion of the Cubes " 262 

62. Filled-in Perception " 263 

63. Double Perception " 263 

64. Hidden Perception " 264 

65. Miiller-Lyer Illusion " 265 

66. Bering Illusion " 265 

67. Perception of Mirror Script " 266 

68. Hedonic Curve XIII 283 



TABLES 

TABLE CHAPTER PAGE 

I. Classification of Science I 6 

II. Vital and Mental Functions II 28 

III. Human Reflexes ^ . . VI 101 

IV. Human Instincts " 106 

V. Instinctive Tendencies of Man " 107 

VI. Progress of Learning VII 123 

VII. Fundamental Operations of Conscious Experience VIII 144 

VIII. Spectral Lines and Color Range IX 165 

IX. Complementary Colors ...'.... " 174 

X. Classes of Odors X 197 

XI. Threshold of Intensity for Taste .... " 201 

XII. Classification of the Senses XI 225 

XIII. Classes of Mental States " 231 

XIV. Values of the Weber Constant XII 258 

XV. Secondary 'Mental States . . . . . . XIV 294 

XVI. Human Emotions " 299 

XVII. Classification of Sentiments " 303 

XVIII. Classes of Associations XVI 343 

XIX. Human Attitudes XVII 362 

XX. Human Dispositions ........ " 367 

XXI. Higher Human Attitudes " 370 

XXII. Classification of Temperaments XVIII 376 

XXIII. Visual Phenomena App. 442 



ACKNOWLEDGMENTS 

The general standpoint adopted in this book was deter- 
mined largely by the writings of David Hartley, James Mill, 
and George Henry Lewes; the influence of these epochal 
thinkers should be acknowledged equally with that of my 
fornier teachers, James McCosh, Wilhelm Wundt, and 
J. Mark Baldwin. The empirical data have been drawn from 
many sources, for the most part too familiar to need special 
mention. Many features of the analysis and classification of 
material may be traced to personal association with William 
James, George T. Ladd, Hugo Munsterberg, E. B. Titchener, 
James R. Angell, Raymond Dodge, Edwin B. Holt, John B. 
Watson, and other workers in the field — even where my 
treatment differs widely from theirs. 

For general suggestions and criticisms I am much indebted 
to my colleagues, Henry C. McComas and Henry L. Eno, 
and to Walter T. Marvin of Rutgers College. In the treat- 
ment of special topics considerable assistance has been given 
by Oliver S. Strong (Columbia), C. F. W. McClure (Prince- 
ton), and S. P. Hayes (Mount Holyoke). 

Thanks are due to Anna Berliner for critical verification of 
data, references, and collateral reading; and to Ulric Dahlgren 
(Princeton), Charles P. Elgin, and Martin Petersen, for draft- 
ing illustrations. I am also indebted to my successive office 
assistants, Naomi S. Peterson, Dorothy Fox, Anna A. Wee- 
lans, and Grace Meng, for their painstaking aid in preparing 
the manuscript and proof. 

Acknowledgments are due to the following authors and pub- 
lishers for permission to make use of illustrations from the 
works mentioned: C. J. Herrick, Introduction to Neurology 
(W. B. Saunders Co.). E. B. Titchener, Textbook of Psy- 
chology, and Experimental Psychology; E. A. Schaefer, Text- 



XX HUMAN PSYCHOLOGY 

book of Physiology; W. B. Pillsbury, Fundamentals of Psy- 
chology; E. B. Wilson, The Cell (Macmillan Co.). E. L. 
Thorndike, Elements of Psychology (A. G. Seiler). J. D. 
Lickley, The Nervous System (Longmans, Green & Co.). 
Joseph Jastrow, Fact and Fable in Psychology (Houghton 
Mifflin Co.). Bailey and Miller, Textbook of Embryology 
(W. Wood & Co.). Gelett Burgess, Nonsense Book (F. A. 
Stokes Co.). C. H. Judd, Laboratory Equipment for Psy- 
chological Experiments (C. H. Judd). E. J. Swift, article 
in Psychological Bulletin (Psychological Review Co.). R. M. 
Yerkes, in Harvard Psychological Studies (Harvard Psycho- 
logical Laboratory). Helen B. Hubbert, in Journal of Ani- 
mal Behavior (Henry Holt & Co.). While the sources from 
which material has been drawn are generally shown in the 
references, special acknowledgment should be made to C. S. 
Sherrington, whose distinction between exteroceptors, inter- 
oceptors, and proprioceptors suggested the classification of 
the senses adapted in this book. 

Princeton, New Jerset 

August, 1919 ' • 



HUMAN PSYCHOLOGY 

CHAPTER I 
THE SCIENCE OF PSYCHOLOGY 

Preliminary Definitions. — Psychology is the scientific in- 
vestigation of mental life. Mental life comprises the events 
which occm* in the active give-and-take relations between 
organisms and their environment. 

These are not intended as final definitions; they indicate in 
a preliminary way the general field which psychology covers. 
First of all we must be sure that we understand the meaning 
of the principal terms in these statements. What is meant 
by scientific investigation, or science ? What is an organism, 
and what are the characteristic features of organization ? 
These notions must be made clear before we can see just what 
is included within the field which we are to investigate. 

Science. — It may seem unnecessary to explain what is 
meant by scientific investigation. But while most of us are 
familiar in a general way with the ' sciences of nature,' we do 
not always realize that the same facts which form the subject- 
matter of science may also be treated in other ways and fall 
outside the province of science. For example, the same ma- 
terial may be used as an instrument for other purposes, or it 
may be studied historically. 

When we take up the study of French, for instance, we may 
propose to become familiar with the structure of the language 
and the general principles or laws of inflection, grammar, and 
the like. This would be a scientific study of the language. On 
the other hand, we may take no interest in this aspect, but 
may wish rather to attain a practical mastery of French in 
order to speak it and to read French literature. In this case 



2 THE SCIENCE OF PSYCHOLOGY 

we are not concerned with the science of French but with 
French as an instrument for acquiring information of other 
sorts. Finally, we may be interested in neither of these as- 
pects of French, but in the historical development of the lan- 
guage. In all three cases the material we deal with is largely 
the same; but the mode of procedure and the facts brought 
out are quite different. The same subject-matter may be 
treated either (1) scientifically, or (2) practically, or (3) his- 
torically. These three view-points lead in any branch to 
Science, Art, and Genetics. 

The distinction just noticed is of greater importance in psy- 
chology than in most branches^ because psychology deals with 
phenomena of our intimate personal life, and its processes are 
used to obtain information of every sort. Mental facts, like 
the French language used in our illustration, may be studied 
in at least three different ways: 

(1) As a science. We may seek to discover the principles 
or laws of mental life and activity, such as the modes of habit 
formation, the laws of association, thinking, etc. 

(2) As an instrument^ to obtain information of other sorts. 
If we wish to understand the nature of the world itself, in- 
cluding matter as well as living creatures, we proceed by 
means of ' rational thinking '; and rational thinking, or logic, 
is a mental process. But when we use logical principles in 
order to miderstand the universe we are not studying mental 
facts as a science, but only as an instrument for philosophical 
research. Or again, we may use psychological principles in 
order to classify human beings on a scale of higher and lower 
intelligence. Here again we are not studying the science of 
mental phenomena — we are merely using the principles of 
mental life as an instrument in investigations of another sort. 
This study is known as applied psychology. 

(3) As an historical growth or development. Mental states 
and processes are subject to change and growth. They differ 
in the child and the human adult ; they exhibit various forms 



SCIENCE 3 

\ 
in different animal species. This historical study constitutes 

a department of study in itself, quite different from the study 

of the principles of mental activity in any one of the stages or 

species. It is called genetic psychology. 

When we speak of the science of psychology it should be made 
perfectly clear whether we are concerned with the static view 
of mental operations as they appear in some definite form of 
being, or with the application of the principles of mental life 
to some other sphere, or with the genetic development of mental 
phenomena. In this book our interest centers mainly upon 
the static view; we are to investigate the phenomena which 
constitute the mental life of adult human beings. 

Classification of Science. — It will help us to understand 
the field of psychology if we consider its relation to the other 
branches which are ordinarily grouped under the generic term 
science. Science means the discovery and systematic formula- 
tion of general truths of nature. The division of science into 
branches is more or less a matter of convenience. Nature is a 
single interworking system of things and events, and hence in 
a way all science is one. But for convenience of study we 
group together those phenomena which are similar in char- 
acter, and we investigate them apart from the rest. Any such 
group is called ' a science.' For example, the properties and 
combinations of elements in a cell are studied in the science 
of chemistry, the play of forces in the science of physics, the 
special activities of cells in the science of physiology. These 
events usually occur at the same time and concern the same 
objects; but the investigator or student examines one set or 
class, assuming or passing over the others for the time being. 

It should be emphasized also that science as such is not 
concerned with individual facts or events. Each event is 
considered as representing any number of similar events, and 
it is especially the interworking of events that interests the 
scientist. The observation of nature in all its phases during 
many centuries has shown us that nature acts uniformly — 



4 THE SCIENCE OF PSYCHOLOGY 

that given the same conditions, the same results follow. 
The doctrine of the ' uniformity of nature ' enables us to 
experiment with individual things and to apply the results of 
these particular observations to all similar things by means of 
generalizations, or ' laws.' 

The most fundamental division of science is into abstract 
and concrete. Abstract science investigates the relations 
which hold equally well for every kind of specific facts. The 
abstract sciences include mathematics in all its branches and 
logic. Quantitative and numerical relations apply alike to 
atoms, masses, forces, and living creatures. What the savage 
or the child discovers by counting his fingers and by adding, 
subtracting, and grouping them in various ways, may be 
applied on a larger scale to the study of the stars and to tables 
of human mortality — in fact to all phenomena. The intelli- 
gent man forms habits of mathematical association and uses 
them in connection with every event of life. These habits- 
are modes of reasoning, and when they are developed into 
an organized system they become a branch of science — or 
a group of such branches. These branches form the abstract 
sciences, or, as they are sometimes called, the mathematiccd 
sciences. They may also be called the general sciences, sincel 
they hold for all classes of natural phenomena. \ 

The concrete sciences deal with phenomena which belong f 
to special phases of nature. They are also often called special' 
sciences or empirical sciences, which points to the fact that the 
truths of nature in each specific field are discovered by ob- 
serving the actual course of events in that field, and not by 
taking the truths discovered in one sphere and applying them 
to another without question. 

Formerly scientists thought it proper to carry over general- 
izations from one field to another in this way. It was assumed 
that the planets revolved in circles on account of the geometri- 
cal simplicity of the circle. Even Newton assumed that there 
must be seven primary colors corresponding to the seven 






CLASSIFICATION OF SCIENCE 5 

tones of the musical scale. We find many such instances 
where early science carried over generalizations from one field 
to another instead of observing the actual course of events. 
This is called the apriori or rational method of investigation. 
At present it has been almost wholly abandoned for the em- 
pirical method in each of the special fields of science. The 
laws of abstract science are still carried over to the various 
concrete sciences; but this is because they have been found 
by repeated observation to apply universally. ^--^^ 

The fundamental concrete sciences are chemistry a,nd physic^. 
Chemistry deals with the relations between specific material 
units; physics deals with the general relations between bodies 
in space and time. At present it is not clear which of these 
two branches is the more fundamental. Probably they are 
coordinate phases of nature, a fact which is expressed in the 
phrase " physicochemical relations." j ^.^ 

"* Biology is another special branch of science, but less funda- 
mental than physics or chemistry. It treats of phenomena 
which appear only in certain special groups of physicochemi- 
cal units called organisms. Coordinate ,.#ith biology_areJhe- 
branches known as astronomy and geology. AH three of these 
branches deal with ' local ' phases of nature which appear on 
the earth or in the universe about us ; they are less general than 
physics and chemistry. Biology is divided for convenience 
into a number of branches, such as zooldgy and bo^tny, which 
need not be discussed here. A more important subdivisio: 
of biology is into the three sciences of morphowgy, physiology, 
and psychology. Morphology deals with the structure and ar-) 
rangement of the various parts and organs of living creatures; 
physiology deals with the internal processes of organisms], 
psychology with their relations to their surroundings. \ 

A further group of sciences deal with the relations between 
separate organisms. These are called the social sciencesr 
They are less fundamental than biology. The science of 
sociology treats of the general interaction among organisms 




6 THE SCIENCE OF PSYgHOLOGY 

of the same species. Human sociology is the most highly de- 
veloped of these branches, because the human species displays 
far greater mutual interaction among its members than any 
other kind of organism. But other species, such as ants and 
bees, may be studied from the same standjf6int. A branch 
closely related to this is social 'psychology, which examines 
psychological data so far as they are modified or affected by 
the social grouping of individuals. Other social branches are 
econojnics, ethics, jurisprudence, etc. [Table I.] 

/ 
,/ Table I. — Classification of Science 

/ / 

^ '' Branches Levels 

1. Abstract (General) : | « MShematics } ^ 



2. Concrete (Special) : 



j Physics 
( Chemistry 



|n 



! Astronomy ^ 

Geology ( i Morphology I jjj 

Biology < ii Physiology f 

( iii Psychology ' J 

( i Sociology ) 

c Social Science < ii Social Psychology >• IV 

' iii Ethics, etc. ) 

Organisms and Organization. — According to this concep- 
tion of the relation of the sciences, psychology is regarded as 
a branch of biology, the science which studies certain sorts 
of units called organisms or living beings. 

Plants and animals taken together form one important 
natural division of the material world. In spite of striking 
differences in size, shape, and modes of activity, all living 
things have certain characteristics in common and differ fun- 
damentally from other forms of matter. The words living 
and lifeless bring out this distinction. Living creatures are 
called organisms, and lifeless matter is called inorganic. What 
do these terms mean.? 

Life is often called a force; but this does not help the explana- 



ORGANISMS AND ORGANIZATION 7 

tion unless we can determine how this force acts and what it 
accomplishes. 

Animals and plants are very complex aggregations of mat- 
ter. They consist of several differentiated organs and usually 
of many segments or members. These parts cooperate in the 
activities of the creature. Organization is the term used to 
denote the peculiar structural and functional ^ relation of 
parts which exists in all animals and plants; it means (1) that 
the parts of a living thing are capable of interaction, and 
(2) that this capacity persists despite growth and changes of 
substance. Life means that the parts (the organs and mem- 
bers) of an organism act in this cooperative way. 

The structure and activities of organisms will be examined 
later. But it may be stated here that the specific forms of 
activity called ' organic ' are those concerned with the con- 
tinuance of the creature's individual existence or with the 
perpetuation of the species. Now the prolongation of exist- 
ence involves two different sorts of process: (1) internal main- 
tenance and growth, and (2) preservation from external de- 
stroying agencies. Thus the activities of organisms may be 
divided into two classes, which we shall call respectively 
growth processes or vitality, and mental processes or men- 
tality. 

(1) Vitality in the broadest sense expresses the fact that an 
organism not only is able to restore its losses and repair its in- 
juries, but that during its earlier life it can become larger and 
more differentiated and in later life can reproduce. (2) Men- 
tality is a term used to express a certain give-and-take rela- 
tionship which exists between an organism and the world 
about. These two characteristics are due to the special 
make-up of organized living creatures. 

Vital Life and Mental Life. — The various activities which 

^ The term structure denotes the composition of a thing and the spatial 
relations between its parts. Function and process denote the manner in 
which the thing acts and its parts interact. 



8 THE SCIENCE OF PSYCHOLOGY 

make up the vital functions of growth and maintenance consti"= 
tute the creature's biological or vital life. We are only in- 
directly concerned with them here. The object of study in 
this book is the relations of give and take between organisms 
and their environment. The facts which arise from these 
relations are the data of psychology. 

If we examine a number of representative organisms, both 
plant and animal, we observe a very marked difference be- 
tween their relations to the world about them and the relations 
of ' inert ' matter to its surroundings. An organism is not 
merely affected by external forces, but on account of its sys- 
tematic organization it is able to control these forces to a 
greater or lesser extent. It receives impressions from the outer 
world, and acts accordingly. This characteristic interaction, 
through stimulation, adjustment, and response, is called 
mentality, and the various activities involved in the process 
make up the creature's mental life.^ 

Among plants interaction with the environment is not 
often apparent; but sometimes it is unmistakable. The 
sun-flower, which turns toward the sun and follows its course 
from east to west, is an instance of stimulation and response. 
So is the sensitive plant, whose leaves close when they are 
touched. 

Animals exhibit this characteristic to a very marked degree. 
Their power of locomotion accentuates the response. The 
lowest species (amoeba and other protozoa) respond to stim- 
ulation by light, heat, and chemical action on their external 
covering, and to mechanical contact or pressure. Sometimes 
the response is positive — that is, toward the source of stimu- 
lation; in other cases it is negative, that is, away from the 
source. 

^ Many terms, such as mentality, impulse, stimulation, sensation, contrast, 
attitude, are used in a precise, technical way by psychologists. Their mean- 
ing is often much narrower or much broader than in popular language. The 
reader should be careful to 'think' them correctly, according to the defi- 
nitions given in the text. 



VITAL LIFE AND MENTAL LIFE 9 

Among higher species of animals we find much more com- 
phcated types of response. When a partridge sees a hunter 
approaching her nest she trails oflf " in an effort to draw him 
away from her young." This is a negative response to the 
visual impression of the man's appearance. When a dog 
sees a rabbit he sets out in pursuit — a positive response 
which finds expression in violent movements of all the bodily 
members. In complex activities like these the response usu- 
ally involves cooperation of many different muscles. 

Self-observation ; Consciousness. — In man, the highest 
animal species, we find the greatest complexity of activity. 
This of itself would give special importance to the study of 
human psychology. But in addition there is a special cir- 
cumstance which broadens the sphere of study. Scientific 
observers belong to the human species. The psychologist can 
not merely observe the responses of human beings and of 
animals generally, but he can study his own relations to the 
environment through self-observation. 

If we examine our own mental life, we find that the effect 
of stimulation by outside forces is something different from 
what we observe in others. When we are affected by a loud 
sound or a brilliant color, we observe the phenomena in a dif- 
ferent way from that in which we observe these forces affect- 
ing the ears or eyes of another human being. More than 
this, we can picture the appearance of a friend when he is miles 
away; and sometimes we form a tolerably accurate idea of 
a coming event long before it happens. There is nothing like 
this in our observations of what animals and other men are 
doing. Your friend's memories are observed by you only in- 
directly — you listen to his verbal description of them, or you 
infer them to be present by the way he acts. Yoiu* own memo- 
ries are a direct and immediate part of your life. 

The experiences which we observe in ourselves either form 
a new set of occurrences to be examined in connection with the 
study of mental life; or else they are another way of looking 



10 THE SCIENCE OF PSYCHOLOGY 

at the same set of facts which we observe in others. The latter 
hypothesis seems more probable.^ However, the question of 
interpretation is far less important than the facts themselves. 
The phenomena of memory, imagination, perception, and the 
like, which we notice in self-observation, are grouped to- 
gether under one general term, conscious phenomena. 

Consciousness and conscious are terms used to characterize 
the phenomena which occur in an individual's own experience, 
so far as these differ from what another individual would note 
in observing him.^ For instance, when my gaze falls on the 
old engraving of Lincoln and his Cabinet I see the figures 
grouped together. I recall certain incidents of Lincoln's life 
and the Civil War. I have an indistinct feeling of attraction 
and admiration. Another person watching me (not the pic- 
ture) would get practically nothing of all this. Possibly if 
he could examine my brain with some fine instrument yet to 
be devised, he would be able to trace out certain chemical 
and molecular changes corresponding to each detail of my 
conscious experience. Consciousness denotes the fact that 
the experience is personal tome (' subjective '), and it includes 
any other distinguishing features of the experience which are 
apparent to me and not to a second person. 

Behavior and Conscious Experience. — The two ways of ob- 
serving the relation between organism and environment in 
man bring out quite different sets of facts. When we study 
the influence of the environment upon some other person 
than ourselves, the effect of stimulation is observed as a re- 
sponse, which takes the form of some characteristic move- 
ment. At a shout, he turns his head and speaks. Seated at 
a table he picks up his knife and fork and conveys food to his 
mouth. Passing a shop window he walks up, stops, and casts 

^ See Appendix, "Subjective and Objective Phenomena," p. 413. 

^ The term conscious, as here defined, is much narrower than the term 
mental. There are many phenomena in mental life which are not open 
to self-observation, and are consequently not characterized as conscious 
phenomena. 



BEHAVIOR AND CONSCIOUS EXPERIENCE 11 

his eyes over the articles displayed. All these obvious move- 
ments, together with many minute muscular adjustments and 
secretion by the glands, are eflFects of the influence of the en- 
vironment on the man; they constitute his response to stimu- 
lation. These motor phenomena, taken together, are called 
behavior. 

A man's (or any animal's) behavior includes the various 
ways in which he acts upon the environment as a result of the 
environment acting upon him. But the word ' act ' is used 
here in a very specific way. If a violent gust of wind strikes a 
man suddenly and blows him down, his movement in falling is 
not behavior, nor is the dent he makes in the ground a response 
— he is not acting upon the environment in an organic man- 
ner. But if he is able to brace himself against the wind and 
avoids falling, or if he puts out his hands to break the fall, 
these movements are instances of behavior; the external force 
in such cases affects him not merely physically but also or- 
ganically — he responds as an organism to the stimulation. 
It is this activity that goes under the name of behavior. 

In psychology, then, we do not study every effect of the 
environment upon the creature, nor every effect produced by 
the creature on the environment, but only the behavior 
phenomena — those movements and changes in which the 
creature is acted upon and responds as an organism.^ 

The second mode of studying mental life is through self- 
observation (commonly called introspection), which examines 
the phenomena of conscious experience. Consciousness phe- 
nomena are the effects of the environment upon the creature 
as they appear to the creature himseff. 

At first glance it might seem as if the facts of conscious expe- 
rience were nothing more than the facts which we study in 
physics and chemistry. When we look at a friend's face, we 
observe an irregular surface broken up into patches of different 

1 The characteristics of the specific type of activity included under be- 
havior are treated in chapters vi and vii. 



12 THE SCIENCE OF PSYCHOLOGY 

colors and shading; these configurations are called the eyes, 
nose, mouth, cheeks, hair, etc. The human features as we 
see them are particles of matter reflecting light. The molec- 
ular composition of the human body, the grouping of the dif- 
ferent cells in space, the reflection of light — all such phenom- 
ena are data which properly belong to physics and chemistry 
and concerning which these sciences have formulated general 
laws and principles. 

But when we study them as effects upon ourselves we are 
dealing with an entirely different set of relations and principles. 
When we look at a human face certain features stand out 
prominent, while others are barely noticed or escape observa- 
tion altogether. The eyes may be the chief object of atten- 
tion. The color of the hair may be noticed casually as part of 
the total impression; a mole on the cheek may remain un- 
noticed; and so of other features. In a word, the face im- 
presses us as a whole, and certain features are vivid items of our 
experience, while other items form a background or fringe of 
fainter impressions. That is, the facts of perception (as this 
type of experience is caUed) stand in quite different relations 
to one another from the physical facts which stimulate us 
through the eye and other organs. The prominence of cer- 
tain features in the human face is not always due to the inten- 
sity of illumination, nor in most cases is the obscurity of 
other features due to their actual lack of physical intensity. 
The difference depends rather upon the internal organization 
of the perceiving creature. Still more do our ' memory 
images ' and our feelings of pleasure, annoyance, hope, and 
desire differ from the physical characteristics of the objects 
which incite them. 

The facts of conscious experience form a different line of 
study from the physical facts of the environment, and the 
processes of conscious experience are quite different from phys- 
ical and chemical processes. These subjective facts and proc- 
esses form an important part of human psychology and their 



BEHAVIOR AND CONSCIOUS EXPERIENCE 13 

study has yielded results far in advance of those obtained by 
the behavior method.^ 

Definition of Psychology. — We are now in position to de- 
fine our field of study more precisely. Psychology is the science 
which deals with the mutual interrelation between an organism 
and its environment.^ The phenomena (occurrences) which 
result from these interactions constitute the mental life of 
organisms, and the characteristic arrangement of structures 
and cooperation of processes which affords this special type 
of interaction is called mental organization. Mental life is 
distinguished from the vital or ' growth ' life of organisms. 
Vital life includes the processes of maintenance, reproduction, 
and the like. These form the subject matter of physiology. 
Only one variety of physiological activity — that of the nerves 
and their terminals — seems at all closely connected with 
human psychology. 

Psychology includes the study of mental life in all kinds 
of organisms. In this book we shall deal with only part of 
the field. Our study is limited to the mental life of man; the 
lower species will be examined only incidentally. The reason 
for this limitation is a practical one. The study of human 
mental life has made considerably more headway than that of 
any lower species, and the human type of experience proves to 
be so far in advance of other types that they can scarcely be 
treated together. Moreover, human mental life can be stud- 
ied by self-observation, as well as by observation of others. 
The former method is not practicable in animal psychology. 

Chief Branches of Psychology. — The divisions of psychol- 
ogy, like those of science in general, are somewhat artificial. 
Nature is more or less a unit, and when we parcel out its facts 
into separate fields it is rather for convenience of study than 
to indicate real barriers between different sorts of natural 

^ They are treated in chapters viii to xviii. 

^ The environment includes all external forces and relations which affect 
the organism — social forces and values as well as physical. 



14 THE SCIENCE OF PSYCHOLOGY 

phenomena. In psychology the sharpest dividing line is 
between genetic (dynamic) and descriptive (static) psychology. 

1. Genetic Psychology is the study of the gradual devel- 
opment of mental life. There are two branches of genetic 
psychology, one dealing with the mental growth of individ- 
uals, the other with mental progress from species to species. If 
we compare a child with an adult we notice at once the differ- 
ence in their mental processes. A child of six months cannot 
dress himself, open a door, use knife and fork, nor perform any 
of the acts common to civilized life which serve to protect one 
from external dangers or promote one's general welfare. The 
growth of mentality in each human individual is gradual. 
The scientific study of individual mental growth is called 
ontogenetic psychology. 

If in the same way we compare human mentality with that 
of lower animals we find corresponding differences and grades 
of progress. Formerly it was supposed that each species of 
animal had a peculiar, specific type of mind, differing from 
that of all other species. Now that the evolution of species 
is generally recognized, these different types of mental life 
are seen to be merely different levels or stages of growth. 
The science of phylogenetic psychology studies the growth or 
evolution of the various mental processes through the chain 
of animal species, from protozoa to man. 

Genetic psychology includes both of these branches. They 
may be investigated separately or together. In the present 
study we shall not take up either of them directly; but the 
meaning of certain mental facts is plainer if we bear in mind 
that mental life is a gradual development and that the mental 
processes found in man are outgrowths of simpler processes 
which maybe observed in subhuman creatures and in children. 

2. Descriptive Psychology, the other main branch of 
psychology, is the study of mental life as it actually exists in 
a species, without special reference to the way in which it has 
come to be. For example, we may examine the nature of hu- 



CHIEF BRANCHES OF PSYCHOLOGY 15 

man speech without considering its growth in the child or the 
race. We may investigate such processes as hearing, imagin- 
ing, thinking, as they actually exist in man without regard 
to their origin and growth. 

Descriptive psychology is the subject matter of this book. 
It is difficult to treat the finished product without touching 
from time to time on its history, but there is no reason why 
we should avoid this problem. Wherever light is thrown upon 
the nature of complex mental phenomena by a study of their 
history, the results of genetic investigation will be taken into 
account. They form an essential part of the analysis. 

Another plan of classification cuts across these lines. We 
may divide psychology according to our method of study. On 
this basis we distinguish between behavior psychology and self- 
observation (or introspective) psychology. Most studies of 
subhuman psychology employ only the behavior method. 
The older text-books on human psychology are based very 
largely on self-observation. But the two methods are closely 
bound together, and psychologists have begun to realize that 
each supplements the other. Both methods are needed if we 
are to obtain a complete understanding of mental life. 

For practical purposes the field of study is usually divided 
into smaller sections. There are text-books and treatises 
which deal with each of the following: 

Human (adult) psychology 

Child psychology . ^ 

Animal (or comparative) psychology 

Abnormal psychology ' 

Physiological psychology ' 

Experimental (or laboratory) psychology^ 

Social psychology 

The first three have already been explained. Abnormal 
psychology treats of the mental life of individuals whose nerv- 
ous system is diseased or imperfectly developed. Physiolog- 
ical psychology makes a special study of the nervous system 



16 THE SCIENCE OF PSYCHOLOGY 

and its operations, in connection with the sensations and other 
mental phenomena that accompany these operations. Ex- 
perimental or laboratory psychology investigates mental phe- 
nomena under precise conditions, usually artificially arranged, 
with the aim of obtaining exact quantitative measurement and 
clear qualitative determinations. Social psychology studies 
the mental phenomena that occur through the mental inter- 
action of individuals in the community. 

In addition there are numerous special branches of psy- 
chology such as psyckophysics, a department of experimental 
psychology which deals with the relation of stimulus to sen- 
sation or perception; race psychology, which examines the 
mental differences between the various human races; and 
religious psychology, which investigates the nature of religious 
experiences. Any topic which is important enough to receive 
separate treatment may be regarded as a branch of the science 
But this list includes all the chief divisions of psychology. 

Collateral Reading: 
James, W., Psychology — Briefer Course, ch. 1. 
Titchener, E. B., Text-Book of Psychology, ch. 1. 
Angell, J. R., Psychology, ch. 1. 
HofFding, H., Outlines of Psychology (trans.), ch. 1. 
Calkins, M. W., First Book in Psychology, ch. 1. 
Yerkes, R. M., Introduction to Psychology, Part I, Part V, 
Watson, J. B., Behavior, ch. 1. 

Pillsbury, W. B., Fundamentals of Psychology, ch. 1. 
Breese, B. B., Psychology, ch. 1. 
Calkins, M. W., Introduction to Psychology, ch. 28. 
Thomson, J. A., Introduction to Science, ch. 4. 
Holmes, S. J., Evolution of Animal Intelligence, ch. 1. 
Morgan, C. L., Introduction to Comparative Psychology, ch. 3. 
Kirkpatrick, E. A., Genetic Psychology, ch. 1. 

Practical Exercises: ^ 

Compare your conscious experience and behavior in copying a sentence. 

Draw up a scheme of the sciences and their relations as they appear to you. 

Observe the behavior of some young child; describe any immaturity of 
mental development; e.g., in handwriting, grammar, table habits, self- 
control, reasoning. 

^ Directions for performing these exercises are given on p. 447. 



CHAPTER II 
THE ORGANISM 

Vital Organization. — Since psychology is one of the 
sciences which deal with living organisms, we shall first of all 
examine the nature of these beings. To understand the con- 
stitution of living creatures we must start from the funda- 
mental facts of chemistry. All matter is made up of some 
83 different elements. Two or more separate particles or 
atoms of these elements combine to form molecules. A mole- 
cule may consist of atoms of the same sort or of different 
sorts. If a molecule contains atoms of different kinds it is 
called a chemical compound. Water is a compound; its mole- 
cules contain two atoms of hydrogen and one of oxygen; this 
is expressed in the formula H^O. 

The chemistry of organisms exhibits several distinctive 
features. 

(a) The molecules which compose the bodies of living crea- 
tures are generally more complex than the molecules of ' in- 
organic ' substances which occur under natural conditions. 
The fundamental element in all organic compounds is carbon. 
Carbon atoms combine with atoms of oxygen, hydrogen, and 
nitrogen, and in a lesser degree with atoms of several other 
sorts, ^ to form organic molecules. 

(6) Organic molecules are very large; that is, they con- 
tain a great number of atoms — far greater than is usual in 
inorganic compounds. For instance the chemical formula for 
albumen is given as C450H720N116S6O140; that is, 450 atoms 
of carbon, 720 of hydrogen, etc.^ In this and other organic 
substances there are over 1000 atoms in each single molecule. 

^ Traces of sodium, potassium, phosphorus, sulphur, calcium, magnesium, 
iron, chlorine, etc., are found in some of these molecules. 
2 Goodchild and Tweney, Technol. and Scient. Die, 1906. 



18 



THE ORGANISM 



The organic compounds which comprise the body of hving 
creatures are known under the name of 'protoplasm. 

(c) Another important characteristic of organic compounds 
is their instability. In the hving organism the protoplasm is 
pecuharly subject to changes of constitution. Its molecules 
are constantly taking in atoms of one sort and releasing those 
of another, or regrouping the atoms in different ways. This 



enclosing two cenirosotnes. 




Plastids lying in the 
cyioplacin 



Karyosome. 
net-knot, or 
chromatin- 
nucleolus 









'asmmm'" 



Fig. 1. — The Cell and its Parts 



Passive bodies (meta. 
pla(>m Of paraplasm) 
suspended io iKec/- 
lopUsniic methwork 



Diagram of an animal cell. The basis consists of a mesh work containing numerous minute 
granules (microsomes) and traversing a transparent ground-substance. [From Wilson.) 



characteristic is of special importance in connection with the 
relation of the organism to its environment. 

(d) Molecules of protoplasm combine to form cells. [Fig. 1,] 
A cell consists of a large number of molecules, usually of many 
sorts. The molecules in a cell are united together somewhat 
like glue or paste. They hang together firmly, but the whole 
group can readily alter its shape; substances of this sort, 
whether organic or inorganic, are called colloids. 

The cell is the unit of organization in living creatures . There 



VITAL ORGANIZATION 



19 



Germ Cell Bone CelU Nerve Cell Receptor Cell 

(Retinal Cone) 

/ 







Mwcle Cells W 




Epithelial Cells 




Blood Cell 




Fig. 2. — Types of Cells 

Spme of the commoner cells which make up the organism. [Drawn from preparations and 
charts; nerve cell from Thorndike.] 

are many different types of cell in the human body — germ 
cells, bone cells, blood cells, epithelial cells, tendon cells, 
muscle cells, nerve cells, and others. [Fig. 2,] These types 
differ considerably in their constitution, but all agree in at 
least two fundamental characteristics: (1) The cell is capable 



20 THE ORGANISM 

of maintaining itself by ingesting material from without and 
casting off its own waste products. (2) It is capable under 
certain conditions of subdividing and thereby reproducing 
new cells. 

(1) The first of these characters involves a two-fold proc- 
ess known as metabolism. When a cell gathers in new ma- 
terial from the environment and builds up fresh compounds, 
the process is known as anabolism. When it becomes active 
and its compounds are torn apart and waste material is thrown 
off, the process is known as katabolism. The two processes of 
anabolism and katabolism are going on constantly in the or- 
ganism — ■ now one, now the other; often the two are taking 
place at the same time in neighboring parts of the organism or 
even in the same cell. This two-fold process of tearing down 
and renewing organic substance results in maintaining the cell 
and (on a larger scale) the organism. Katabolism is accom- 
panied by activity and discharge of energy, while anabolism 
replenishes the energy of the cells and stores it up for future 
use. Thus metabolism maintains the activity of organic life 
as well as the constituent matter of the organism. 

(2) The second property of the cell is known as mitosis, or 
division. Under certain conditions, by means of a compli- 
cated process, a cell subdivides into two complete cello, 
which may or may not be similar to each other. In the case 
of germ cells this subdivision marks the beginning of a new 
and independent organism. Both of the resulting cells hence- 
forth maintain a separate existence. In other types of mito- 
sis the multiplying process continues but tho resulting cells 
remain grouped together, forming a multicellular creature. 

If the resulting cells are similar they may remain very 
closely bound together, forming a bone, a muscle, a skin sur- 
face, etc. When such an organ or structure is once formed, if 
the subdivision of cells continues the organ gradually increases 
in size but preserves the same general shape. This is illus- 
trated by the growth of the bones in childhood. Mitosis also 



VITAL ORGANIZATION 21 

generates new cells to replace those which are destroyed or re- 
moved by the accidents of life. In addition to repairing the 
ordinary wear and tear of skin, nails, and other tissues, this 
effect is seen in the wide-spread renewal of substance lost 
through a wound. In every case the biological result of mito- 
sis is the same — the production of new cells. 

In the lowest plants and animals the organism or creature 
consists of a single cell, which in cooperation with the environ- 
ment performs all the various processes involved in mainte- 
nance and reproduction. These single-celled organisms are 
known as protophyta (plants) and protozoa (animals). In 
higher species of plants and animals the individual consists 
of a large number of specialized cells grouped together so as to 
form a unitary organism. These complex creatures are known 
as metaphyta (plants) and metazoa (animals). Each indi- 
vidual of the many-celled species starts as a single cell, which 
divides and redivides over and over again. As the subdivi- 
sion proceeds the cells become differentiated and specialized 
in various ways; the cells of each type go to make up some 
special kind of organ, which performs some specific sort of 
function. For example, a large number of cells of a very 
special sort unite to form a bone. The system or group of 
bones taken together serve to maintain the structural rigidity 
of the body, and at the same time serve as levers in the per- 
formance of various bodily movements. Similarly, epithelial 
cells unite to form the skin, etc. Each type serves to fulfil 
some special function in the life of the organism. [See Fig. 2.] 

Organisms of the higher types perform a large number of 
distinct physiological processes, such as breathing, circulation 
of blood, digestion, secretion. Looked at from a broad 
standpoint these are all variations or modes of the general 
vital processes of maintenance and reproduction. Many of 
these subsidiary processes cooperate in a single act, as for ex- 
ample the various activities concerned in eating and in diges- 
tion. It is this cooperation of structures and processes that 



22 THE ORGANISM 

constitutes the creature's organization. A creature, whethei 
animal or plant, which is able to maintain itself and to repro- 
duce through its structural arrangements and through the 
resulting cooperation of functions, is termed a biological or- 
ganism. The complex system of structure and functions which 
characterizes living creatures is called vital organization. 

A living organism is capable of growth and structural 
change. Its various parts (structure) are capable of per- 
forming the many acts or processes concerned in mainte- 
nance and reproduction, while the processes operate to 
create and preserve the structure. This interplay of struc- 
ture and process, of organ and activity, extends in an endless 
series throughout the lifetime of the individual. 

Classes of Vital Functions. — The processes of maintenance 
and reproduction are termed physiological or vital functions. 
These life processes are not due to a mysterious vital force 
or personality seated within the cell. ^ They are chemical and 
physical changes. Any specific vital act, such as eating, usu- 
ally involves a number of different processes (e.g., chewing, 
salivation, swallowing, etc.). In the last analysis each of 
these component processes consists of one or more series of 
chemical and physical activities which take place within the 
organism. This transformation and displacement of sub- 
stance (so far as we can determine) is fundamentally the 
same as that which occurs in the inorganic world. But owing 
to the complex constitution of protoplasm and its remarkable 
instability, there are certain characteristic differences between 
organisms and inorganic bodies. (1) The physiological activ- 
ity of living beings is exceedingly complicated; (2) it affects 
the whole organism; and (3) it generally results in a better 
adjustment of the creature to his general situation. 

While the vital functions may all be grouped together under 
the two general heads of maintenance and reproduction, it 

^ See Appendix, "Purpose in Organic Growth," p. 425; "Personification 
of Natural Phenomena," p. 433. 



CLASSES OF VITAL FUNCTIONS 2S 

is convenient to subdivide them more specifically according 
to the special duties which they perform. Biologists recog- 
nize a great number of specific vital processes, such as breath- 
ing, circulation, digestion, sucking, grasping, chewing, leg 
movements, winking, and a host of others. A study of these 
would be interesting, but it belongs to general physiology and 
does not especially concern us here. 

The generic functions of maintenance and reproduction are 
found to include a number of distinct sorts of process. We 
may distinguish altogether six great classes of vital functions:^ 

Organization (i.e., unitary interrelation of parts) 

Nutrition 

Growth (i.e., increase in size) 

Regulation 

Repair (or regeneration) 

Reproduction 

The meaning of organization and reproduction has already 
been explained, and the distinction between nutrition and 
growth is too obvious to require discussion. Regulation is a 
term used to denote the capacity of organisms to adjust them- 
selves to variations in temperature, change of diet, and the 
like. Repair is their capacity to heal injuries and to make 
good the loss of parts occurring beyond the ordinary wear and 
tear of life.^ 

Psychologists are interested in the vital functions chiefly 
on account of the sharp contrast they offer to the functions 
which make up mental life. All the types of activities just 
listed serve primarily to maintain the body substance and 
energy of the organism. There are other types of process 
which serve to establish an interrelation between the organ- 
ism and its environment. These are called mental functions. 

^ The term function as used here and elsewhere in the book means any 
generic process, or general kind of process. The term process is used for the 
specific kinds. Nutrition is a generic process which includes a great variety 
of specific processes such as chewing, swallowing, etc. 

2 The term regeneration is used when a new organ or part similar to the old 
is grown. 



24 THE ORGANISM 

Mental Organization. — Most organisms, in addition to 
maintaining themselves and reproducing, are able to adapt 
themselves in some degree to the changes which take place in 
their environment, and many of them are able to produce 
very significant modifications of the environment. 

The act of nutrition, in a narrow sense, involves merely 
absorption of matter and chemical energy from the immediate 
surroundings of the creature. But even simple one-celled 
organisms like amoeba wander about and may be said to ex- 
plore the environment for their nutriment. In the same way 
(though by means of far more complex processes) the human 
being enters into active relations with the world about him. 
He goes fishing or hunting or plants a garden to obtain food; 
or if he lives in a civilized community he walks over to the 
market and buys food. All this means the establishment of 
special kinds of relation with the environment. These ac- 
tivities serve to enlarge a man's points of contact with his 
surroundings; they often result in substituting one set of 
surroundings for another. . 

A crab which has lost its claw is able to grow a new one. 
This is merely a complicated vital process. But an animal be- 
longing to a higher species may dodge to one side and thereby 
avoid a blow which would have resulted in severing his arm 
or leg. Activity of this type prevents the occurrence of injury 
instead of repairing its effects. 

The functions of which these are examples are different in 
type from the functions of nutrition, repair, etc. They in- 
volve activity on the part of the organism in relation to cer- 
tain features of the environment. But the interplay ordi- 
narily reaches farther than this. When we build a house or 
use any sort of tool we are actively engaged in modifying our 
environment. 

In man the 'environment' is tremendously broadened in 
both space and time. An architect living in New York may 
direct the construction of a building in San Francisco. The 



MENTAL ORGANIZATION 25 

environment upon which he acts extends at least over that 
range of territory. When a farmer plants his field in the spring 
he is acting in reference to the crops which will appear in the 
summer or fall. His environment is thus extended to include 
a section of the future. 

All creatures are capable to some extent of adapting them- 
selves to varying conditions in their environment, and the 
higher species are capable of modifying the world about them 
in many significant ways. In the more complex species this 
mutual interworking is accomplished by means of certain 
specialized structures within the creature — the nervous sys- 
tem and its terminal organs. ^ But even in the absence of such 
differentiated organs a similar interaction occurs. The pro- 
tozoa, or one-celled animals, though they possess no differen- 
tiated nervous system, are able to receive impressions from the 
environment and to affect or alter the environment in many 
ways. They show at least a rudimentary differentiation of 
structure. 

The interaction between an organism and its environment 
actually involves three stages: stimulation, adjustment, and 
response.^ Each single interaction may be called an experi- 
ence, and the sum-total of such experiences make up the 
mental life of the organism. The special structures and types 
of function which bring about the interaction constitute his 
mental (or psychical) organization.^ 

The relation between structure and function is different 
here from what we found in the case of vital organization. 
In mental life the functions do not build up the structure. 
Mental processes do not produce the nervous system, though 
they may modify its finer structure to some degree. The 
special organs concerned in mental life are the result of vital 
activity, working upon inherited organic material. They are 

1 See ch. iii. ^ See ch. v. 

' Many writers restrict the terms psychical and mental to conscious states 
and processes. 



^6 THE ORGANISM 

due to the vital functions of reproduction and growth. In 
other words, mental life makes use of the structure built up 
by vital processes; it uses them not for growth or reproduc- 
tion, but for adaptation to conditions in the outer world. 

Classes of Mental Functions. — Any movement or internal 
change which occurs in an organism either directly or in- 
directly as a result of stimulation may be regarded as a ' re- 
sponse,' and the chain of activity involved in the experience 
constitutes a ' mental process ' in the broadest sense of the 
term. If we take account of all the muscles and glands, as 
well as the special organs for receiving stimulation in man, 
we find a great number of distinct varieties of mental proc- 
esses. But usually both the stimulation and the responsive 
activities occur in groups. Even such a simple response as 
winking involves the cooperation of muscles in both eye-lids, 
and in most cases it is brought about by stimulation of a 
large area in the eye. 

Mental processes may be classified according to their com- 
plexity and with reference to the result wtiich they accomplish. 
Among the simpler mental activities are winking, swallowing, 
yawning, and many other types. The complex forms of men- 
tal processes in man include such acts as walking, eating, 
display of anger, fear-activity, talking. In civilized man 
the manifestations of mentality become exceedingly complex; 
they embrace such intricate activities as planning out a vaca- 
tion, running a business, and governing a nation. Each sepa- 
rate type of process may be investigated by observation and 
experiment. In later chapters we shall examine some of the 
distinctive varieties of mental activities; at present we are in- 
terested in determining the general difference between vital 
and mental processes. 

We noticed that the vital functions may be grouped under 
a few general headings. In the same way the mental func- 
tions, despite their tremendous variety, may be grouped to- 
gether into six general classes. The most fundamental 



CLASSES OF MENTAL FUNCTIONS 27 

type of mental function is (1) simple response to stimulation. 
This is exhibited in the tropisms of the lower species and the 
reflexes of many-celled organisms. The knee-jerk, sneezing, 
and winking are typical reflexes. Higher in complexity are 
the two functions known as (2) instinct and (3) habit, which 
bring about adaptation through the cooperation of several 
reflex mechanisms. Instincts are built up by evolution in the 
race and transmitted to the individual by inheritance; habits 
are acquired separately by each individual. The suckling ac- 
tivity of infants is a typical instinct; opening a door and type- 
writing are examples of habit. A fourth class of mental proc- 
esses is (4) communication; it is not more complex than habit 
or instinct, but it constitutes a distinct type, since it is con- 
cerned with the interrelation of separate organisms. An in- 
stance of this is answering a question. Still another type of 
mental function is (5) rational action, and last of all the far- 
reaching system of activity known as (6) social conduct. 

These different classes of mental functions differ essentially 
from the vital processes already enumerated. There is, how- 
ever, one border-line case. The locomotor functions, though 
generally concerned with the active relations of organisms to 
their environment, are sometimes wholly vital in character. 
The ordinary life condition of the one-celled Paramecium is 
locomotor activity. Irrespective of external stimulation its 
cilia are in constant movement and it normally moves along 
in a spiral course. This enables it to take in food without any 
special adjustment. When it meets an obstacle it stops and 
reverses its movement; but its normal forward movement is 
not a response to external stimulation; it is as much a part of 
the creature's vital life as growth and nutrition. In higher 
organisms, however, locomotion usually occurs as a response 
to stimulation and may be classed among the instincts or 
habits. 

For the sake of comparison a list of the two sorts of functions 
is given in Table 11, 



28 THE ORGANISM 

Table II. — Vital and Mental Functions 
Vital Functions Mental Functions 

Organization Simple Response (Tropism and Reflex) 

Nutrition ' Instinct 

Growth Habit 

Regulation Communication 

Repair Rational Action 

Reproduction " Conduct 

Locomotion 

Evolution of Mental Life in Organisms. — Plants manifest 
very slight adaptation to their environment through stimula- 
tion and response. The growth of complexity from lower to 
higher species is almost wholly on the vital side. Among ani- 
mals, however, there is a steady increase in complexity of 
adapt9,tion through behavior as we ascend the scale of life; 
mental life assumes greater and greater importance as com- 
pared with vital life in the creature's total existence. 

By far the most complex adaptations appear in man. He 
receives a countless variety of stimuli and his responses are 
tremendously intricate and far reaching. In civilized man 
mental life is the preponderant factor. Even the vital func- 
tions of nutrition and reproduction tend to become subor- 
dinated to impulses of mental life. The small boy who misses 
his dinner in order to see a base-ball game and the religious 
ascetic who renounces matrimony in order to cultivate holi- 
ness and humility, are merely exaggerated instances of the 
increasingly important role of mental life* which we find in all 
higher beings. 

Mental Life as Psychobiological Organization. — As ex- 
plained in the first chapter, the province of psychology is the 
investigation of mental life. The psychologist seeks to under- 
stand the processes involved in stimulation and response, to- 
gether with the modes of adjustment between these two. The 
entire chain of activity summed up in stimulation, plus ad- 
justment, plus response, constitutes experience. The investiga< 
tion of mental life is the study of experience, whether that 



PSYCHOBIOLOGICAL ORGANIZATION 29 

experience is accompanied by any discoverable consciousness 
or not. 

In the human species the behavior phenomena, which are 
the active manifestation of mental life, are known to be ac- 
companied by consciousness; in other cases its presence is 
doubtful. It is a question how far we should assume or infer 
the presence of consciousness when it is not directly reported. 
We are not especially concerned with this problem in the 
present book, since we are dealing with normal adult human 
beings, who are capable of reporting their conscious experi- 
ences. But if we seek to bring our human study into rela- 
tion with animal psychology it is important to adopt a definite 
viewpoint. 

While the presence of consciousness in subhuman animals 
is not demonstrated, the evidence indicates that the mental 
life of man is merely a higher or more complex form of the 
same sort of phenomena which appear in lower species. The 
evolution process is gradual, and starts at least with the pro- 
tozoa. We seem justified, then, in assuming that conscious 
experience of some sort exists in all forms of animal life where 
behavior activity occurs. 

On the other hand it is admitted by all investigators that' 
no mental life has been observed except in animals and pos- 
sibly plants. That is, the only beings which manifest mental 
life are biological organisms. Psychology, then, deals with 
psychohiological organisms and studies the phenomena of 
psychobiological organization . 

Summary of Chapters I and II. — We may sum up briefly 
the points which have been brought out in these first two 
chapters. Psychology is the science of mental life; that is, 
the science which investigates the interrelations between or- 
ganisms and their environment. Mental life consists in the 
adaptations of an organism to changing conditions of its en- 
vironment, and the processes which bring about these adap- 
tations constitute experience. Experience includes behavior 



30 THE ORGANISM 

and consciousness — behavior being the action of the crea- 
ture upon his environment, and consciousness an effect of en- 
vironment on the creature. 

Mental hfe is characteristic of living organisms. So far as 
we know, it belongs only to these. The organization of such 
beings is two-fold — vital and mental. Vital functions are 
those which serve to maintain the individual existence of an 
organism or to perpetuate the species. These functions may 
be classed under several general heads: organization, nutri- 
tion, growth, regulation, repair, and reproduction. Mental 
functions comprise all activities which bring about interac- 
tion between the organism and its environment through the 
chain of processes called stimulation, adjustment, and re- 
sponse. Mental functions may be grouped into several gen- 
eral classes: simple response, instinct, habit, communication, 
rational action, and conduct. The function of locomotion is 
both vital and mental. Mental life increases in importance 
as we ascend the scale of species. In man it may even re- 
place the vital life as the chief factor of his existence. 

Mental functions operate through certain bodily structures 
and organs which are built up by vital processes. Like other 
types of bodily structure these are composed of protoplasm. 
In all higher organisms, including man, the structure con- 
cerned in mental life is highly differentiated and consists of a 
complex connecting system of pathways called nerves and of 
specialized organs for receiving impressions and producing 
motor activity. The nervous system and its terminal organs 
constitute the structural basis of mental life. 

Collateral Reading : 

Moore, B., Origin and Nature of Life, esp. chs. 5-7, 9. 

Osborn, H. F., Origin and Evolution of Life, Introduction. 

Mathews, A. P., Physiological Chemistry, ch. 1. 

McKendrick, J. G., Principles of Physiology, chs. 2, 3. 

Wilson, E. B., The Cell. 

Lickley, J. D., The Nervous System, ch. 1. 

Morgan, C. C, Animal Life and Intelligence, 2d ed., chs. 1-3. 



SUMMARY 31 

Hobhouse, L. T., Mind in Evolution, 2d ed., chs. 2, 3. 
Parmelee, M., Science of Human Behavior, ch. 2. 

Bawden, H. H., Evolution of Behavior, Psychol. Review, 1919, 26, 
247-76. 

Practical Exercises: 

What has been your notion of "a mind"? 

Describe some observations of your own on the repair of organisms (human 

or other). 
Analyze the simple movements which compose some common habit; e.g. 

putting on a hat or taking off a glove. 



CHAPTER III 
THE NEURO-TERMINAL MECHANISM 

Structural Basis of Mental Life. — The interaction between 
man and his environment is effected by means of certain 
specially differentiated cells which are peculiarly adapted to 
produce the chain of activity described in the preceding 
chapter. These cells may be divided into three classes. 

(1) Cells of the first type — which include many very dif- 
ferent varieties — are so constituted that they are set into 
activity (' stimulated ') by forces of one sort or another in the 
surrounding world or within the body. These are called re- 
ceptor cells, or receptors. In some cases a number of differen- 
tiated cells form a special receptor organ, such as the eye or 
the ear. 

(2) The second type of cell is peculiarly adapted to transmit 
the effect of stimulation in the form of impulses from the re- 
ceptors to centers within the body, from one center to another, 
and from the centers toward the periphery of the body. These 
differentiated cells are called nerve cells or neurons. 

(3) The third class of cells includes two varieties; one is 
peculiarly fitted to contract, the other to produce chemical 
substances (' secretions ') when affected by impulses from the 
neurons connected with them. Both types are called effector 
cells, or effectors. Effectors of the first sort are grouped to- 
gether to form a muscle or contractile organ; those of the 
second sort constitute the glands or secretory organs. 

The process of mental activity is based upon these three 
diSfferent organs — receptors, neurons, and effectors — which 
are arranged in a chain. The receptors and the effectors form 
the two ends of the chain and are called the terminal organs ; 
the neurons which connect these terminals constitute a, nerv- 



STRUCTURAL BASIS OF MENTAL LIFE 33 



ous arc. A nervous arc with its terminal organs form a neuro- 
terminal circuit. [Fig. 3.] 




-spinal lemniscus 
correlation neuron 1 
funiculus dorsalis 

r~^ sp.g.l 
correlation neuron; 2 
sp.g.2 

•-^ sKin 

/ ) sp.g.3 

correJation neuron 5 

O sp-g.4- 
B 



Fig. 3. — Neuro-Terminal Circuits 

A. Simple circuit from receptor in skin through cord to muscle. [From Her- 
rick, modified after Van Gehuchten.] 

B. Several circuits through cord; portion of complex circuit through higher cen- 
tera indicated by vertical arrow at top; m = muscles. [From Herrick.] 





34 THE NEURO-TERMINAL MECHANISM 



L .Oendritn 



The sum total of neurons in the body,^ which consist of 
a net-work of interconnected arcs, is called the nervous sys- 
tem. The entire system of neurons and terminal organs, 
which constitutes the structural basis of mental life, may be 
called the neuro-terminal mechanism. In examining the 
structure of this very elaborate mechanism it will be conven- 
ient to describe the nervous system first, since it forms by far 
the most important part of the circuit. 

Nervous System ; Structure of the Neuron. — In all ani- 
mals there are special paths of conduction for incoming and 
outgoing impulses. Even the protozoa 
have pathways within their body which 
conduct more readily than the rest of 
their protoplasm. In many-celled ani- 
mals (metazoa) these lines of conduction 
are made up of neurons, which are com- 
posed of a highly specialized kind of 
protoplasm. 

The general structure of the neuron 
is shown in the accompanying diagram. 
[Fig. 4.] In most other types of cell the 
•central body is the largest and most 
significant part; but in the nerve cell 
the body is far less important than the 
projections or 'processes.' As the nerve 
cell grows, it sends out a long thread, 
called the nerve fiber or axon, usually with 
one or more branches called collaterals. 
The extremities of the axon and colla- 
terals usually terminate in an arboriza- 
tion,^ branching and rebranching like a 
tree. The arborization near the cell 
body is very intricate and is called the deridrites ; the farther 

^ Together with certain other elements, such as connective tissue and glia. 
^ This arborization is sometimes called the end brush. 




Fig. 4. — The Neuron 
AND ITS Parts 



STRUCTURE OF THE NEURON 35 

end of the axon is called the telodendrion. The cell body, axon, 
collaterals, telodendrion, and dendrites make up the neuron. 

Neurons vary exceedingly in size. Some of the connecting 
sensory fibers in the spine are very short; they may be of 
microscopic size. Many neurons are very long; the sensory 
fibers from the toes to the spine are over two feet in length. 
There are several different sorts of neurons, varying in the size 
of their cell body and in the number and arrangement of their 
projections. They bear distinctive names, such as unipolar, 
bipolar, multipolar, pyramidal, Purkinje cells, etc. [Fig. 5.] 
Different types of neurons are found in the afferent (sensory) 
and efferent (motor) portions of the chain, and several dis- 
tinct kinds occur in the central region. 

Most of the growth of neurons takes places in embryonic 
life. At birth they have nearly reached their normal number 
and size. After birth relatively few neurons are added to 
the system, compared with the total number, and the growth 
of the existing neurons merely keeps pace with the general 
growth of the body. 

Each nervous arc consists of several neurons connected to- 
gether on the relay principle. One end of a sensory neuron 
extends out from the cell body till it almost reaches the sur- 
face of the body, where it connects with some receptor organ. 
In the other direction the same cell sends our projections 
which (in most cases) terminate in a mass of nervous tissues 
forming the spinal cord. Almost in immediate contact with 
this latter end is another neuron or neurons, which relay with 
a series of neurons extending up the spinal cord into the 
brain. This relay system serves to transmit an impulse from 
a receptor organ to the brain. A corresponding chain of re- 
layed neurons transmits motor impulses from the brain to a 
muscle or gland. These two conducting lines, called sensory 
and motor paths respectively, are connected by the mass of 
central neurons which make up the brain itself. A shorter 
relay connects the two lines in the spinal cord. [See Fig. 3.] 




Fig. 5. — Types of Neurons 

Above, six neurons of various types. Note the relative size of cell body and axon; the thick- 
ness of the axon is exaggerated and the finer arborization does not always show in the drawing. 

Below, a Purkinje cell, greatly magnified. This type, found in the cerebellum, is charac- 
terized by elaborate branching of the dendrites; the axon (below, to the right) extends beyond 
the limits of the drawing. [From Thorndike; lower cell after KoUiker.J 



STRUCTURE OF THE NEURON 



37 




Fig. 6. — Synapses 

A basket cell from the cerebellar cortex of a rat, showing synaptic connections 
of a single neuron (B) with several neurons (A). A typical synapse is shown at a. 
b = terminus of axon, c = axon of basket cell. [From Herrick, after Ramon y Cajal.J 



The separate neu- 
rons which make up 
the circuit or Hue of 
conduction are not 
completely joined 
together. The telo- 
dendrionic arboriza- 
tion of one neuron 
intermeshes with the 
dendrites of the next, 
but according to the 
best observation 
there is no connect- 
ingfilament between 
the two. The region 
where two neurons 
intermesh is called 
a synapse. There 
are several types of 
synapse. [Figs. 6, 7.] 




S' 




Fig. 7. — Synapses 

Various types of synapses; the synaptic regions are shown 
at S. [From Thorndike, after Van Gehuchten.l 



38 THE NEURO-TERMINAL MECHANISM 

In addition to the main lines of conduction along the axons, 
the collaterals furnish alternative paths of transmission. 
Within the brain especially the collaterals and arborization 
of one neuron form synapses with the dendrites of several 
other neurons, so that the whole brain presents a ramified 
mass — somewhat as an electric lighting system branches out 
in every direction. This branching and these alternative 
paths are especially significant in the interpretation of neural 
activity. 

In some types of neuron the cell body lies slightly off of 
the direct line of transmission. [Cf. two right-hand cells 
in Fig. 5.] Possibly the nerve impulse in such cases does not 
pass through the cell body at all. This has led to the view 
that the cell body of the neurons is concerned chiefly with the 
growth and maintenance of the neurons and not essentially 
with the specialized function of nervous conduction. 

Cerebrospinal System : General Plan. — The neurons are 
not scattered promiscuously through the body, but are massed 
in certain definite regions and lie side by side during the 
greater part of their coUrse. The brain and spinal cord, in 
particular, consist of masses of neurons running parallel or 
connected end to end or crossing one another singly and in 
groups. These great masses of nerve substance comprise the 
central nervous system. Sensory and motor fibers connect the - 
central system with the receptors and effectors respectively. 
The brain, cord, and these peripheral connections are called 
the cerebrospinal system. [Figs. 8, 9.] There are also certain 
groups of neurons which form a more or less independent sys- 
tem, though connected with the rest. This is called the sym- 
pathetic or autonomic system, which will be treated later. 
[Fig. 9.] The cerebrospinal and autonomic systems, taken 
together, constitute the nervous system. 

The peripheral neurons which link up the receptors and 
effectors with the central system are not scattered and dis- 
persed except near the terminals. They are grouped together 



CEREBROSPINAL SYSTEM 



39 



in bundles called nerves. For example, the separate afferent or 
sensory neuron fibers which originate in various parts of the 
retina in the eye unite to form a trunk line called the optic 
or second cranial nerve, which con- 
nects the eye with the optic center 
in the brain. Similarly the separate 
fibers from the auditory apparatus 
and semicircular canals in the ear 
run side by side in a bundle which 
forms the eighth cranial nerve. The 
afferent fibers which originate in the 
skin below the neck are collected 
into a number of bundles which 
terminate inside the. spinal cord en- 
closed in the back-bone; two affer- 
ent or sensory bundles (i.e., one 
from the right side and one from 
the left) enter at each interstice be- 
tween the vertebrse. 

The outgoing neurons are gathered 
together in the same way. A bundle 
called an efferent or motor nerve, 
consisting of many separate nerve 
fibers, starts at some center in the 
brain or in the spinal cord and passes 
out through one of the openings be- 
tween the vertebrae. These motor 
fibers run along side by side for a 
time in company with the sensory 

Fig. 8. — Central Cerebrospinal System 

Above, the brain, including cerebrum, cerebellum 
(CBL), and medulla (MED). The spinal cord extends 
downward from medulla and is indicated by projecting 
nerves, cut off in the drawing; C I to C VIII = cervical 
nerves; TH I to TH XII = thoracic; L I to L V = lum- 
bar; S I to S V = sacral; COC I = coccygeal. 




40 



THE NEURO-TERMINAL MECHANISM 



1 

CAVOLUTED CORD { 




I cEsncAi msvB 



I THORACIC HERVX 



LUMBAR HERVB 



-t SACRAl HSRVS 



VI COCCYQEAl, NBRVS 



FILUH TEE MIX ALE 



Fig. 9. — Cerebrospinal System and Sympathetic Ganglia 

Ventral view of brain and cord. The sympathetic ganglia are shown in black at left. [From 
Herrick, after Allen Thompson and Bauber.J 



CEREBROSPINAL SYSTEM 41 

fibers.^ As they approach the terminal organ the separate 
fibers part company and lead to different parts of the muscle. 

In the case of both sensory and motor nerves the separate 
fibers or neurons running side by side in the bundle are insu- 
lated from one another; a nerve impulse in transit does not 
pass across from one fiber to any of its parallel neighbors. 

The bundles of fibers (nerves) originating in the head [Fig. 
13] and cord [Fig. 9] are named and numbered with reference 
to their point of origin. In all there are 12 pairs of cranial 
nerves, and 31 double pairs (sensory and motor) of nerves 
leading to or from the spinal cord. Each nerve contains a 
great many separate fibers. 

Owing to the collateral connections there are many more 
possible paths of conduction than there are separate lines of 
fibers. At certain points in the chain of afferent neurons there 
are direct connections with efferent neurons. These occur, 
for example, at or near the point of entry into the cord.- 
[See Fig. 3.] Through these collateral connections an incom- 
ing impulse may pass directly across and out to some motor 
organ without traveling up to the brain. In other words, it 
forms a short-circuit. 

Of far greater importance, however, is the vast system of 
interconnections which exist in the brain. The human brain 
contains many billions of connecting neurons; these serve to 
connect sometimes one, sometimes another sensory neuron (or 
group of neurons) with now one, now another group of motor 
neurons. It would be difficult to calculate the total number 
of possible connections which might be made in the human 
brain. We may liken the brain to a telephone exchange, in 
which any one of thousands of subscribers may be joined up 
with any other. The analogy is not quite correct, since sen- 
sory neurons are never joined with other sensory neurons in 
complete circuit. If we suppose our telephone wires divided 

^ The sensory and motor nerves are sometimes called centripetal and 
cerdrifugcd, respectively. 



42 THE NEURO-TERMINAL MECHANISM 



lJ— ^— tL_— c 




Pig. 10. — Paths in Cord and Brain 

Diagram showing course of some of the principal paths for conduction of afferent and efferent 
impulses. [From Bailey and Miller.] 



THE SPINAL CORD 43 

into two groups, those which receive messages but do not 
respond, and those which make calls but never receive mes- 
sages, the analogy will hold. 

The Spinal Cord. — With exception of the nerves of the 
autonomic system ^ all the peripheral nerves of the body below 
the head, but including the neck, enter the back-bone or spine 
in the spaces between the separate vertebrae, as described 
above. The bones of the spine enclose a canal or channel, 
which contains a mass of neurons leading to and from the head 
and neurons leading laterally across. The mass of neurons 
within the spine form a long cord which extends from the 
coccyx to the head and is called the spinal cord. The cord is 
very small iii, diameter near the lower end, and increases in 
thickness (with some variations) as more nerves enter it at 
each successive vertebral opening. [See Fig. 9.] 

The roots of the sensory nerves enter the dorsal (back) sur- 
face of the cord, while the motor nerves enter the ventral 
(front) surface. The paths connecting the peripheral nerves 
with the brain cross over in the cord from right to left or 
from left to right; so that the neurons terminating in the left 
side of the body connect with centers in the right side of the 
brain, and vice versa. The general course of the principal 
afferent and efferent paths in the cord and brain are shown 
diagrammatically in Fig. 10. 

If we examine a cross-section of the cord [Fig. 11] we ob- 
serve that the center appears grayish, and the surrounding 
portions light colored. The gray matter, as it is called, con- 
sists of cell bodies and fibers, while the surrounding white 
matter consists practically only of nerve fibers. The gray 
matter of the cord viewed in cross-section looks roughly like 
an H. The dorsal part of each ' upright ' of the H contains 
sensory cells which receive the fibers of the right and left 
sensory roots respectively; the ventral portions of the uprights 
contain cells which send out the fibers of the motor roots. 

^ See p. 49. 



44 



THE NEURO-TERMINAL MECHANISM 



The sensory and motor paths of the same side connect, com- 
pleting the uprights of the H, and the sensory paths cross 

from side to side, forming the 
cross-bar of the H. 

The nerve fibers which pass 
up and down the cord form 
the white matter. The sepa- 
rate nerves lose their identity 
within the cord; the fibers are 
grouped together into great 
masses called tracts, which are 
composed in part of continu- 
ations of the nerves, and 
in part of fibers of neurons 
belonging to the cord and 
brain. 

We may note that the dor- 
sal (sensory) ends of the H 
are usually "pointed while the 
ventral (motor) ends are hlunt 
and rounded. This difference 
is due to the fact that the cell 
bodies of the peripheral sen- 
sory neurons lie outside the 
cord.^ Only the cell bodies 
of certain connecting sensory 
neurons lie within. The cell 
bodies of the peripheral mo- 
tor neurons, on the contrary, 
lie inside the cord. Hence 
there is a larger mass of gray 
matter (cell bodies) in the ventral than in the dorsal region. 
The Brain. — The higher connecting system, or brain, is 
exceedingly intricate in man. Practically the whole interior 

^ They form the spinal ganglia. 




Fig. 11. — Cross-Section of Cord 

Central gray matter (G) surrounded by- 
white matter (W). From the ventral horn 
(VH) of gray matter emerges the motor root 
(MR) of a spinal nerve (SP.); the sensOry 
root (SR) of same nerve enters the dorsal 
horn (DH) which is more pointed than the 
ventral. Near the junction of the two roots 
is the spinal ganglion (SG) of sensory cell 
bodies. 

The nerve shown in the figure is on the left 
side of body; the roots of the corresponding 
right-side nerve join the cord at the further 
pair of horns. [Modified from Testut.l 




Fig. 15. — Cortex, from Above 

Showing the hemispheres, separated by medial fissure. FL = frontal lobe; ACC = an- 
terior central convolution; RF = Rolandic fissure; PCC = posterior central convolution; 
PL = parietal lobe; OL = occipital lobe. 




Fig. 12. — Model of Human Brain 

Photograph of detachable model in papier-mache by Th. L. Auzoux. 




Fig. 13. — Base of Brain 

I'rom below, looking upwards. Cranial nerves are labeled (right) and numbered (left). 
[From Striimpell and Jakob.) 




m 



BO i 

to a 



Mi 



?; 


•" 


o 


j;"o 


H 




u 


J3 Z 


w 


a >a 


rn 




r^ 


y m 


"A 


^ i^ 




« 

n 


2| 






ta a 



THE BRAIN 45 

of the skull back of the mouth and above it is filled with a 
mass of neurons whose fibers interconnect in an exceedingly 
complex fashion. It has been estimated that there are at 
least 9280 million neurons in the cerebral cortex alone (the 
outer layer of the upper brain mass). 

The lower part of the brain [Fig. 12, cf. Figs. 8 and 9] ^ 
begins just above the level of the mouth as a swelling of the 
spinal cord; this enlargement is called the medulla oblongata. 
Back of the medulla and connected with it lies a spherical 
mass called the cerebellum [Fig. 13], while anterior to the me- 
dulla (forward) and somewhat above the cerebellum is a band- 
like mass crossing laterally called the pons Varolii.^ The cere- 
bellum is a coordinating center for movements concerned in 
maintaining equilibrium and general motor control of the 
body. Above the cerebellum and pons the medulla is lost in 
a number of odd-shaped masses of neurons called the basal 
ganglia or basal masses of nuclei [Figs. 13, 14], which are made 
up in part of fibers from the medulla prolonged upward, and 
partly of the cranial nerve fibers which connect with recep- 
tors and effectors in the head. 

Of the twelve pairs of cranial nerves [Fig. 13], some 
are entirely sensory (the optic, auditory, olfactory), others 
wholly motor (the oculomotor and other nerves connecting 
with the eye muscles, the hypoglossal connecting with the 
tongue muscles), while several contain both sensory and 
motor fibers (the facial, for facial expression and for taste, 
the trigeminal for the skin receptors in the face and for the 

^ The relation of parts in the brain can scarcely be understood without 
examining a model. If one is available it should be studied instead of the 
figures given in the text. The same is true of the eye and ear, described 
in chapters ix and x. 

2 The medulla, cerebellum, and pons constitute the hind-hrain ; certain 
of the basal masses form the mid-brain ; the cerebrum and remaining masses 
make up the fore-brain. These terms are based on the evolutionary history 
of the brain, which though of prime importance in comparative psychology 
lies beyond our present field. Consult references at end of chapter, espe- 
cially Lickley and Donaldson. 



46 THE NEURO-TERMINAL MECHANISM 

muscles used in mastication). The cranial nerves terminate 
in the basal masses. 

Above the basal masses and cerebellum, and covering them, 
are two great masses (right and left) called the cerebrum or 
cerebral hemispheres, which are separated by a deep cleft 
called the medial fissure. The outer (gray) layer of the 
cerebrum is called the cortex. The cortex is spread out directly 
under the skull, following its general contour. 

The Cortex. — The cerebral cortex deserves special exami- 
nation. [Figs. 15, 16.] The most striking feature about the 
cortex is its wrinkled character. The outer surface is creased 
into rounded ledges and fissures in various directions, so that 
there is considerably more * exposed ' area than if it were 
smooth. 

The relation between white and gray matter in the cere- 
bral hemispheres is the reverse of that in the cord: the gray 
matter lies on the outside, the white matter inside and beneath. 
Since the gray substance consists chiefiy of cell bodies, it is 
evident that the outer layer or cortex of the cerebrum con- 
tains a mass of cells, while the underlying portion consists of 
fibers passing in various directions. The cortex is only 2 to 
4 mm. in thickness, but on account of the folds it has a very 
large superficial area. It plays a role of great importance in 
mental life, particularly in the higher and more complex 
mental operations. 

The two hemispheres are connected beneath by a great 
bridge of nerve fibers called the corpus callosum. The tracts 
of fibers which pass through the callosum generally terminate 
in corresponding regions of the two hemispheres; they thus 
serve to connect any given region in the left hemisphere with 
the symmetiically situated region in the right. The fibers 
which connect the two hemispheres are called commissure 
fibers. There are also tracts of fibers which connect one re- 
gion in either hemisphere with other regions or centers in the 
same hemisphere. These are called association fibers and 



THE CORTEX 47 

tracts. The commissure and association fibers constitute the 
central or internuncial pathways of the hemispheres. 

The cortex is divided by its fissures into several rather 
distinct masses called lohes. Morphologists have named 
these the frontal, parietal, occipital, and temporal lobes ; they 
correspond in the two hemispheres. The dividing lines be- 
tween the lobes in some cases are very clear. Notice (Figs. 
15 and 16) the central or Rolandic fissure which separates 
the frontal from the parietal lobe, and the Sylvian fissure 
(Fig. 16) which separates the temporal lobe from these 
two. The boundaries of the occipital lobe are less definite. 
As a matter of fact the division into lobes does not neces- 
sarily denote any specific functional difference; they are 
named rather for convenience in topographical study. The 
same is true of the separate folds or convolutions into which 
each lobe is divided. 

The cortex consists of quite a number of regions (centers 
or areas) in which fibers of one sort or another terminate. 
These regions may be grouped into two main classes, (a) pro- 
jection areas and (&) association areas. The projection areas 
are the terminals of fibers coming from the primary sensory 
centers or nuclei in the basal masses and of fibers leading from 
the cortex to the primary motor centers in the basal masses. 
The association areas are centers for fibers coming together 
from two or more projection centers. The projection areas 
serve to integrate impulses coming from similar receptors and 
to coordinate impulses which operate groups of muscles, while 
the association areas serve to integrate and coordinate differ- 
ent sorts of sensory and motor impulses. A typical projec- 
tion area is found in the region lying both front and back of the 
Rolandic fissure. The areas in front of this fissure are found 
to be centers for movement of different parts of the body, 
while those back of the same fissure are centers for sensory 
paths from the receptors in the skin. These two areas are 
motor and sensory projection centers, respectively. [Fig. 17. 



48 



THE NEURO-TERMINAL MECHANISM 



Note the subdivision of these areas according to the differ- 
ent regions of the body with which they connect.] 

Most of the projection areas are grouped together in three 
distinct regions of the cortex: (1) About the Rolandic fissure, 
extending from the crown of the head downward on the side. 




Fig. 17. — Projection Areas in Cortex 

Outer surface of left hemisphere, viewed from left, showing projection areas along 
Rolandic fissure, and speech centers. [From Herrick, after Starr.] 

(2) In the occipital lobe at the extreme back of the head. 

(3) In the underlying portion of the temporal lobe toward the 
center of the head. 

The association areas lie between these. [Fig. 18,] (1) 
There is a large association region in the frontal lobe covering 
nearly the entire frontal portion of the cortex. The other 
association areas are not so definitely established. They are 
believed to include: (2) An association region comprising a 
large portion of the temporal lobe. (3) An association re- 
gion in the frontal lobe near the top of the head. (4) An as- 
sociation region connecting (2) and (3). (5) A region in the 
fore part of the occipital lobe which is an extension of (2), (3), 
and (4). 



THE CORTEX 



49 



These tracts contain the highest loops in the system of 
nervous arcs. They serve to connect together a great 
number of receptors and a great number of effectors and 
unite them into very complex circuits. The cerebral cortex 
is the ' inmost central link ' in the chain of neurons which 
form the pathway from the receptors to the effectors. 




Fig. 18. — Association Fibers in Cortex 

[From Lickley.] 

Autonomic System. — In addition to the nervous path- 
ways leading through the spinal column to the brain, there 
are conducting neurons called sympathetic nerves or sym- 
pathetic ganglia, which lie outside the spine and somewhat 
anterior to it. [Fig. 19, cf. Fig. 9.] They consist of several 
collections of nerve cells (ganglia), one near each vertebra, 
with fibers which extend in various directions. (1) Fibers 
from these ganglia form a pathway to the internal organs for 
digestion, circulation, etc. (2) Each ganglion is connected 
with the next higher and next lower ganglion, (3) They are 
also connected with the cord by efferent fibers from the latter. 
The two sets of sympathetic ganglia (one on the right side, 
one on the left) extend up as far as the head. There are also 



i(f tenieal ganglion of tympathttic 




Pharyngeal placuli 

UUdlt cervteal ganglion of 

sympathetic 
Inferior cervical ganglion of 
_ tympalhetis 



\^Thoracie 
plexuses 



Abdominal 
plezuaes 



Pelvic 
flemt^a 



Fig. 19. — Autonomic System 

Showing sympathetic ganglia and plexuses. Numbering of nerves corresponds to that of 
the «rebrospinal system; cf . Figs. 8, 9. [From L^ckley. after Schwalbe.] 



AUTONOMIC SYSTEM 51 

similar ganglia within the head, and important nerve groups 
(plexuses) in various parts of the body. The three main 
plexuses are (1) at the base of the heart, (2) in the upper part 
of the abdominal cavity, (3) in front of the lowest lumbar 
vertebra. 

The sympathetic nerves serve to control the vital ' nutri- 
tive ' processes of circulation, digestion, and breathing. The 
entire system of sympathetic ganglia and plexuses is called 
the autonomic system. Since the autonomic system is con- 
nected at a multitude of points with the cerebrospinal sys- 
tem, nerve impulses constantly pass from one to the other. 
Through this interplay our mental activities are constantly 
affecting our vital activities and our vital processes modify 
our mental processes. Thus the autonomic system, though 
chiefly concerned with vital functions, assists in the opera- 
tions of mental life, especially in connection with the ' sys- 
temic ' states which will be discussed later. 

Terminal Organs. — The specialized cells which lie at the 
two extremes of the nervous pathways are not nerve cells, but 
they serve as intermediaries between the neurons and the 
forces of the environment. The cells at the beginning of the 
arc (receptors) are radically different in structure from those 
which lie at its terminus- (effectors). 

I. Receptors. — The receptor cells and receptor organs are 
of many different sorts. Each receptor is a specialized struc- 
ture, which is capable of being affected by one (and usually 
by only one) of the many kinds of force which exist in the en- 
vironment; when thus stimulated it starts a nerve impulse 
in the neighboring sensory neuron. We distinguish between 
complex receptors, such as the eye and the ear (which are com- 
posed of a number of different parts and consist of several 
different kinds of cells) and simple receptors, such as the 
Meissner and Krause corpuscles for cutaneous sensations. 
[See Figs. 30, 43, 54.] 

The structure of the different sorts of receptors will be 



52 THE NEURO-TERMINAL MECHANISM 

treated in connection with the central sensory data which 
they yield (ch. ix, x) . It should be noted that there are con- 
siderably more than five kinds of receptors, and that the 
historic classification into five senses is quite inadequate. The 
following different receptor organs, with corresponding senses, 
can certainly be distinguished : visual, auditory, static, olfac- 
tory, gustatory, tactile, warmth, cold, kinesthetic, and organic. 
In addition, the reception of pain stimuli can occur directly in 
the sensory pain-nerves without an intermediate receptor. 

2. Effectors : Muscles and Glands. — The other class of 
terminal organs, known as effectors, lie at the peripheral ter- 
minals of the motor nerves. They comprise two very dis- 
tinct types, muscles and glands. 

A muscle consists of fibers of contractile tissue, bound to- 
gether into a belt of strands and attached at each end to some 
bone or other tissue. [Fig. 20.] When a nerve impulse 
reaches the peripheral terminal of a motor nerve, the energy 
is transmitted to the strands of muscle and causes the whole 
muscle to contract in length and enlarge in diameter. The 
two ends of the muscle are thus brought nearer together and 
this produces a movement of the member to which the muscle 
is attached.^ 

For example, the biceps muscle of the arm is attached at the 
lower end to the radius bone some distance below the elbow. 
When this muscle contracts the radius is pulled upward and 
the whole forearm describes a circular arc with the elbow joint 
as center. Another muscle on the outer side of the elbow 
serves to pull the arm in the opposite direction and straighten 
it out again. The former movement is called flexion, the 
latter extension. Most muscles occur in pairs, one counter- 
acting the other. Such pairs are termed antagonistic muscles. 

Notice that in muscular activity the force is applied to the 

^ The nerve impulse starts a chemical process in the muscle, releasing 
energy. The total energy represented in muscular activity is far greater 
than that of the nerve energy which touches it ofiF. 



EFFECTORS: MUSCLES AND GLANDS 



53 



lever arm near the fulcrum, and the long end of the lever per- 
forms the action. A suit-case is lifted in the hand, while the 
contracting muscle operates near the elbow. This is the op- 
posite of the ordinary use of the lever. In mechanics the force 
is usually applied at the long end of the lever arm, which en- 



%. ^'- 



f /A 











Fig. 20. — Muscle, with Nerve Endings 

Striate (voluntary) muscle, showing how motor nerve fibers terminate in the 
several strands. [From Dunlap.] 

ables us to lift a heavy weight at the short end with com- 
paratively slight effort. The fact that the great muscles in 
the arm are capable of raising very heavy weights at the long 
lever-end will give some idea of their extraordinary strength. 
Not all of the muscles are attached to bones ; the eye muscles, 
for example, are attached at one end to the eyeball itself, 
which is not a bony structure. 



54 THE NEURO-TERMINAL MECHANISM 

The muscles of man are of two different structural types, 
called striate (striped) and smooth. The striate muscles, 
with exception of the cardiac or heart muscle, are all supplied 
by motor nerves of the cerebrospinal system. From the func- 
tional standpoint they are called voluntary muscles, because 
their activity is under the direct control of the brain mechan- 
ism. The smooth muscles are found in the internal organs 
and are connected with the autonomic system. Physiologi- 
cally they are termed non-voluntary muscles. The cardiac 
muscle is striate, but it is supplied by the autonomic system 
and is classed as non- voluntary.^ 

Every definite movement which we make, whether great 
or small, is the result of muscular contraction. The muscles 
are located all over the body. Some are very large, others 
exceedingly minute, their size varying with the activities 
which they have to perform. Each muscle is separate from 
the others, though in some cases they cross. The complex 
movements which we make are not due directly to coopera- 
tion between the muscles concerned, but to coordination of 
impulses in the motor nerves and centers. 

A gland is a mechanism for separating from the body fluids 
certain materials out of which it may also build up new chem- 
ical substances. This process is called secretion. A gland is 
composed of specialized cells, which bring about chemical 
analysis and synthesis among certain substances. One sort of 
gland acts upon the substances which compose saliva. When 
it operates, saliva is formed. Another sort of gland secretes 
tears, another urine, another sweat, etc. Some types of 
glands are furnished with ducts which carry off the secre- 
tions. Others, called the ductless glands, secrete various 
chemical substances (hormones) used in the growth and 
maintenance of the body. 

^ The terms voluntary and non-voluntary are. somewhat confusing in this 
connection. The ear muscle is striate and supplied by cerebrospinal fibers, 
but in most men ear-twitching is not a voluntary act. The fimctional dis- 
tinction is clearer if we divide muscles into cerebrospinal and autonomic. 



EFFECTORS: MUSCLES AND GLANDS 55 

When a nerve impulse passes along an efferent nerve which 
connects with a gland, the energy is transmitted to the gland 
and induces its specific activity. The secretory action of the 
tear glands may be started in a child by a motor impulse orig- 
inating in the stimulus caused by bumping his head; in an 
adult the activity of the sweat glands may be set into opera- 
tion by a motor impulse due to the perception of being in a 
dangerous situation. For the most part, glandular activity 
is connected with the vital processes and does not concern us 
here. But in situations like those just cited it constitutes an 
important factor in the interaction between the organism and 
its environment. 

Summing up briefly, the neuro-terminal mechanism con- 
sists of the nervous system with its specialized terminal organs, 
the receptors and effectors. In this chapter we have examined 
the structure of this mechanism, particularly the cerebrospinal 
nervous system. In the following chapters we shall take up 
the modes of activity and operation of the neuro-terminal 
mechanism. 

Collateral Reading : 
Lickley, J. D., Nervous System, esp. chs. 2-7. 
Herrick, C. J., Introduction to Neurology, chs. 3, 7-10, 16, 19. 
Piersol, G. A., Human Anatomy, Vol. II., pp. 996-1380. 
Ladd and Woodworth, Physiological Psychology, Part I, chs. 1-5, 9. 
Dunlap, K., Psychobiology, chs. 3-8. 
Donaldson, H. H., Growth of the Brain, chs. 7, 8, 10, 13. 
Wilder, H. H., History of the Human Body, ch. 10. 
Harris, D. F., Nerves, ch. 1. 

Starling, E. H., Principles of Human Physiology, chs. 6, 7. 
Stiles, P. G., The Nervous System and its Conservation, chs. 2, 5. 
Angell, J. R., Psychology, ch. 2. 
Judd, C. H., Psychology — General Introduction (2d ed.) chs. 2, 3. 

Practical Exercises: 

Describe (or name) the different sorts of muscular movement which you 

can observe in your face and head. 
Analyze the location of touch, warmth, cold, and pain, as found in some 

region of your skin. 
Report any instances of 'physical exhaustion,' indigestion, etc., due to 

worry, or of gloomy outlook due .to digestive trouble. 



CHAPTER IV 
PHYSIOLOGY OF THE NEURON 

Functional View of the Nervous System. — The nervous 
system comprises all the neurons in the body. Viewed as a 
working machine it consists of all possible circuits (nervous 
arcs) which may be joined up by combining various sensory, 
central, and motor neuron-chains. For psychologists the in- 
terest in this mechanism lies in the fact that it serves as a 
medium for the interaction between the organism and its en- 
vironment. The environment affects the creature through 
the activity of the nervous mechanism, and the creature is 
able to produce changes in the environment by the same 
means. It is therefore of considerable importance for us to 
understand how the nervous mechanism works. 

We shall examine the operation of the nervous system in 
the following order: (1) The activity of individual neurons; 
this includes an examination of the nature of the nerve im- 
pulse and the fundamental operations in nerve substance 
which produce differences in the impulse (ch. iv). (2) The 
specific operations which take place in each part of the ner- 
vous arc (ch. v). (3) The operation of the nervous arc as 
a whole, and the manner in which it serves to promote inter- 
action between a creature and its environment (chs. vi, vii). 
The activity in the nervous arc, together with the muscular 
contractions, movements, and secretory changes which re- 
sult from this activity, constitute the creature's behavior. 

The Nerve Impulse : Intensity and Mode. — Very little 
is definitely known as yet regarding the nature of the specific 
activity which takes place in the neurons. The propagation 
of energy (called nerve impulse) certainly does not involve a 
transfer of physical particles, like the flow of water through 
a pipe. Neither does the phenomenon (so far as we can judge) 



NERVE IMPULSE: INTENSITY AND MODE 57 

consist wholly in a wave motion of molecules, like sound or 
other effects of jarring which occur in the air or other media. 
Investigation has shown that electrical disturbances occur in 
the nerve substance during the passage of impulses ; but there 
are indications also that chemical changes take place during 
the operation. Which of these processes is the characteristic 
feature of the nerve impulse is still in dispute.^ 

The specific form of any impulse seems to depend upon the 
specific form of activity in the receptors, which is determined 
by the nature of the stimulus, though this is also challenged. 
In all but the primary sensory neuron it certainly depends, in 
part at least, upon resistance at the synapses, and possibly 
upon other local factors. We may distinguish two sorts of 
variation in the impulse : differences in intensity and differences 
in mode. 

(a) Intensity of the Nerve Impulse : The intensity of an 
impulse at any point is measured by the amount of activity 
at that point in a unit of time. Neurons have a certain range 
of capacity for receiving impulses. If the stimulus is very 
intense it affects the neuron only up to a certain limit, the 
remainder of the disturbance passing over into other tissues. 
In this respect the phenomenon does resemble the flow of 
water in a pipe; beyond a certain limit the conductor is un- 
able to take care of the water — the surplus overflows into the 
surrounding territory. On the other hand if the stimulus is 
very weak it is unable to overcome the resistance at the junc- 
tion between receptor and nerve, and does not excite activity 
in the sensory neuron at all. Similarly, a weak impulse in 
any neuron may be blocked by the resistance at its synapses, 
so that no excitation is produced in the next neuron. Thus 
we find an upper and a lower limit to the intensity of nerve 
impulses. 

Where two impulses from different neurons come together 

^ See Appendix, "Nature and Modal Variations of the Nerve Impulse," 
p. 435. 



58 PHYSIOLOGY OF THE NEURON 

in a single higher neuron of the chain, the impulse in the 
latter is a summation of the two, and may be more intense 
than either of its components. 

(6) Mode of the Nerve Impulse: In neurons connected 
directly with receptors the impulse appears to vary also with 
the mode of stimulation. For example, the eye is capable of 
stimulation by light waves of any frequency between about 
399 and 768 trillion per second. Waves in the neighborhood 
of 400 trillion produce a certain form of impulse which is ex- 
perienced as ' red sensation ' when the effect reaches the brain. 
Waves in the neighborhood of 520 trillion produce a different 
effect known as yellow, etc. Different rates (modes) of wave 
vibration between the two limits produce varying modes of 
impulses in the optic nerve, while in most eyes waves which 
are more frequent than 769 or less frequent than 399 
trillion per second produce no observable effect whatever. 
Similar variations in mode occur in the auditory and other 
sensory nerves. There are far greater modal differences be- 
tween impulses in different sorts of sensory nerves than occur 
in nerves of the same class. For example, there are many 
modes of impulse in the optic nerve, but all these ' visual im- 
pulses ' resemble one another far more than they resemble any 
' auditory impulse.' 

The mode of the nerve impulse may be pictured as due to a 
specific rate or frequency in the succession of elementary im- 
pulses, just as the mode of a given light wave or sound wave 
is due to the frequency of ether vibrations or air vibrations. 
Or it may be conceived as a variation in the chemical processes 
which take place during neural activity. 

What little information we possess regarding modal differ- 
ences of neural activity is not obtained directly from meas- 
urement of impulses in the neurons. It is derived from the 
conscious experiences which follow stimulation, and these 
experiences indicate only the character of the impulse in the 
central cells which lie in the brain. 



THE NERVE IMPULSE 59 

It is questioned indeed by many writers whether any modal 
differences exist among sensory impulses. The observed dif- 
ferences among sensations have been attributed to specific 
modes of energy supposed to characterize the different types 
of cells in various centers. According to another view they 
are due entirely to the 'patterns into which impulses are com- 
bined in the centers. The general relation between varia- 
tions in stimuli and variations in sensations appear to support 
the view here outlined, that modal differences exist among 
impulses in the sensory nerves. We cannot regard the ques- 
tion as finally settled, however, till the precise nature of the 
nerve impulse is determined.^ 

The impulse in the motor nerves varies only in intensity ; or 
if variation in mode exists it produces no noticeable effect on 
the muscles or glands. The intensity or degree of the motor 
impulse determines the rate of muscular contraction; if the 
muscle is called upon to perform more work (in lifting a weight) , 
the same speed of muscular contraction requires a more in- 
tense degree of motor impulse. The only noticeable difference 
in mode among motor nerve impulses is between direct and 
inhibitory excitation. In certain cases, following an ' active ' 
impulse, a ' checking ' impulse appears to be sent down the 
same motor path, which counteracts the effect of the active 
excitation. 

Fundamental Operations of Nerve Substance. — The sub- 
stance which composes the neuron is capable of two specific 
types of operation in addition to those which bring about 
growth and repair. These specific properties of nerve are 
called excitability (or irritability) and conductivity. Excitation 
means that nerve substance is capable of being stirred to ac- 
tivity in some way as a result of receiving energy from without. 
Conduction means that after such excitation the nerve sub- 
stance is capable of transmitting an impulse along the nerve 

^ See Appendix, "Nature and Modal Variations of the Nerve Impulse," 
p. 435. 



60 PHYSIOLOGY OF THE NEURON 

fiber from one end of the axon to the other, and to the end of 
its collateral branches. In addition to excitation and con- 
duction there are certain factors which serve to determine 
the nature of the nerve impulse in a given neuron, and which 
therefore belong among the fundamental operations of nerves. 
There are in all seven kinds of operation: 

Excitation 
Conduction 
- Retention 

Metabolic variation 
Summation 
Distribution 
Modification 

I, Excitation. — Except in a few special cases the physical 
and chemical forces which operate in the environment do not 
act directly upon the nerve substance. They affect some one 
of the various sorts of specialized receptor organs, and the 
activity of these receptors produces excitation in the neigh- 
boring neuron. This process is known as stimulation (ch. v.). 
The excitation of all succeeding neurons in the chain consists 
of taking up an impulse from some other neuron. Activity 
is aroused in the sensory neurons of the cord (and in other 
secondary sensory neurons) by impulses received from the 
primary sensory neurons. The primary central neurons are 
excited by the sensory neurons in the cord (or by cranial sen- 
sory neurons); other central neurons receive their impulse 
from the primary central neurons. The motor neurons are 
excited either by an impulse from some central neuron or by 
sensory activity in the cord. 

The process of excitation is not gradual, like the metabolism 
which takes place in ordinary vital functions (nutrition, etc.). 
It is of the ' explosive ' type. The entire excitation is set up 
almost instantaneously, like touching off gunpowder. Thus 
the two kinds of activity (nutrition and excitation) which take 
place in nerve, though they may occur simultaneously, are 
quite distinct. 



EXCITATION 61 

The excitation process works upon potential energy ' stored ' 
in the nerve cell and uses it up. A nerve which has just re- 
ceived an excitation is incapable of receiving another immedi- 
ately. The delay (called the refractory period) is short, in 
some cases only 0.002 second. 

Much still remains to be discovered about the nature of ex- 
citation. It appears that the impulse aroused in a secondary 
neuron may at times be more intense than that in the neuron 
from which it derives the excitation. To this extent the gun- 
powder analogy holds. On the other hand, the intensity of 
excitation is apparently in most instances proportional to that 
of the stimulus, which would not be the case if the entire la- 
tent energy in each nerve were ' set off ' by the stimulus or 
by the passage of an impulse from the preceding neuron. 
We have here two phenomena, which at present do not ap- 
parently quite harmonize: (1) The intensity of excitation is 
proportional to the intensity of stimulation. (2) The inten- 
sity of excitation varies according to the energy present in 
the neuron excited. 

2. Conduction. — The second property of nerve substance 
is conduction; or ability to propagate impulses. When a 
neuron has been excited at one end, the impulse passes along 
the axon to the other end and travels also along the collat- 
erals, so that the entire neuron is progressively excited. The 
rate of nerve conduction varies in different types of nerve and 
in different species of animals. In the sheathed nerves of the 
frog the rate is from 24 to 38 meters per second, while in un- 
sheathed nerves it is much slower — from 0.2 to 8 meters per 
second. In the sheathed nerves of man the impulse may 
travel as rapidly as 125 meters per second ^ or perhaps even 
faster. The sheathing acts as an insulator and prevents loss 
of energy in transmission. 

When the impulse reaches the far terminal of the neuron it 

^ Herrick, Introd. to Neurol., 2d ed., p. 104. The tates of conduction in 
animals and man reported by various investigators dififer considerably. 



62 PHYSIOLOGY OF THE NEURON 

passes through the synapse into the next neuron, provided the 
substance of the synapse be in such condition as to permit the 
impulse to overcome the resistance at that point. It may also 
pass through the synapses of some of the collaterals into 
branch-paths. Conduction means that a neuron is capable of 
conducting an impulse (due to excitation) from a receiving 
end to a discharging end, and of discharging it into the next 
neuron. 

In the living nervous system each neuron conducts impulses 
in one direction only: sensory neurons always transmit im- 
pulses away from the periphery toward the center, and motor 
neurons transmit from the center toward the periphery. In 
experiments upon isolated (excised) neurons it has been found 
that an impulse which starts in the middle of the neuron will 
travel in either direction. The fact that the living nerve 
conducts only in one direction is apparently due to something 
in the nature of the synapse.^ Either the ' near terminal ' 
is only able to receive impulses and is not capable of sending 
them back across the neighboring synapse ; or the ' far termi- 
nal ' is only able to transmit impulses into the synapse beyond 
and is not capable of receiving them; or both of these may be 
true. The synapses in any case serve to check the backward 
jflow of the nerve impulse.^ They are somewhat like the 
rotary gates which we find in some of our subway exits, which 
allow passengers to go out but prevent -them from coming in. 

The phenomenon of conduction concludes with the dis- 
charge of impulses at the further end. After this has taken 
place the discharging neuron becomes quiescent, and the 
neuron next in line takes up the impulse and propagates it 
along. It appears from physiological experiments upon nerves 
that if the discharge once begins, and a portion of the impulse 

^ There may also be a property of living nerve which renders the conduc- 
tion irreversible in direction. The experiments showing reversibility were 
performed on isolated nerves. (See Herrick, op. cit., p. 103.) 

* See L. Luciani, Human Physiol., p. 201. 



CONDUCTION 63 

passes through, the transfer continues till all the energy passes 
over into the next neuron. In other words, if any energy at all 
passes across the synapse, the entire amount of kinetic energy 
represented by the impulse passes across, so that the first 
neuron is completely drained. This is known as the all-or- 
none law. It may be compared to the action of a syphon, 
which does not start to work till the liquid attains a certain 
level and then discharges the entire contents of the vessel. 

It should be borne in mind that nerve conduction is not a 
transfer of material substance from end to end in the nerve. 
The phrase ' nerve current ' is only a figure of speech. The 
conduction is probably some sort of chemical change, accom- 
panied by electrical disturbance, which is transmitted like 
a wave from point to point till it reaches the end of the 
neurons. 

3. Retention. — The passage of a nerve impulse through 
the neuron tends to produce a change of some sort in the sub- 
stance.^ The exact nature of this alteration is not yet known; 
but it is known that nerve substance somehow retains the 
effects of excitation. When an excitation is repeated the out- 
come is often very different the second time from the first. 
The first excitation has left a trace or set which persists long 
after the impulse is gone. The effect of these retention traces 
is observed constantly in the behavior of animals and men as 
well as in one's own personal experiences. According to 
Lloyd Morgan {Habit and Instinct, p. 41), when a chick has 
picked up an inedible caterpillar and rejected it, if it comes 
upon a similar caterpillar again it will seldom pick it up a 
second time, though the stimulus and excitation are the same 
as before. 

Observation of the learning process in man shows constant 
changes due to the persistence of traces. The same effect 
appears elsewhere. A memory image is apparently due to 
repetition of the mode which characterized some former im- 

^ See Appendix, "Retention, Metabolism, and Modification," p. 437. 



(54 PHYSIOLOGY OF THE NEURON 

pulse; but memory occurs when no external stimuli are pres- 
ent such as gave rise to the experience originally. The mode 
of the memory image is thus apparently determined by the 
retention trace. A slight retention effect is found also when 
the same sensory stimulus is repeated again and again; it is 
observed as a ' feeling of familiarity,' which characterizes the 
experience. 

As a result of the retention of traces in the nerve substance 
new sensory impulses tend to assume the same mode as the old. 
The trace may exert a greater or lesser influence upon the new 
impulse according to circumstances. The retention effects in 
the optic nerve, for example, are generic as well as specific. 
Visual impulses exhibit a great variety of different modes, 
all of which belong to one general class — the ' luminous.' In 
the adult, who has received innumerable visual stimuli, any 
excitation of the optic nerve tends to take on the generic 
' luminous ' mode. A blow on the head results in our seeing 
a flash or splurge of light. 

The retention effect in the central and motor neurons con- 
sists in part at least in the formation of a more or less perma- 
nent connection at certain synapses. When the resistance 
at a synapse is overcome and the impulse passes across, the 
path becomes ' worn down ' so that subsequent impulses pass 
more readily along this path than before. Permanent lines 
of lessened resistance are thus established, which bring about 
the formation of habits. 

It is difficult to account for the variety of alternative move- 
ments which occur in many habitual activities on this basis 
entirely. A slight variation in the stimulus will at times alter 
the whole character of the act. In typewriting, each of the 
different letters seen in the manuscript leads to a specific 
movement. It seems probable that the quality or mode of 
the stimulus is a factor in determining the combination of 
movements which enter into a given response. 

The retention of the traces of former modes of excitation 



RETENTION 65 

in the central and motor neurons would account for this, even 
though the mode of the impulse has no effect upon muscular 
contraction. If a motor neuron has once received an impulse 
of a certain mode, it will retain the effect of this mode. If 
later on another impulse of the same mode occurs in the central 
neurons, it will pass into a motor neuron which has retained 
this kind of trace, rather than into other neurons whose 'set ' is 
different. We may conceive of the process by the analogy of 
several doors, each of which is opened by a certain particular 
key; or we may liken the motor neurons to a set of tuning 
forks, each of which vibrates sympathetically to a certain 
rate. However we picture it, the essential feature of the proc- 
ess is that one motor neuron or another receives the central 
impulse according as its retention trace is the same in mode 
as the present central impulse. 

There has been considerable dispute as to whether reten- 
tion effects are ineradicable — whether every impulse leaves 
a permanent mark in the nerve substance. No definite 
answer to this question can be given at present. There are 
indications that motor tendencies continue to persist even 
though the specific connections have not been made for a 
long time. Once a person has learned to swim, to telegraph, 
or to perform any other motor act, the effect of such motor 
combinations is observed after years of disuse. There is also 
abundant evidence to show that a retention effect in the 
central neurons may persist for many years. Instances are 
known where very old persons have recalled incidents of early 
youth and childhood, which had in all probability never been 
revived in the meanwhile. If a chance connection shows this 
persistence in a few cases, there are probably many more which 
only await the proper excitation. 

Some writers go so far as to assert that every excitation 
leaves a permanent effect — that no experience is ever really 
forgotten. This sweeping assertion, however, goes far be- - 
yond the evidence, since in the nature of things it is only the 



66 PHYSIOLOGY OF THE NEURON 

uneradicated effects that are brought to light. For every ef- 
fect which lasts to old age there may be a thousand others 
which time has wiped out entirely. The evidence certainly 
indicates that many retention effects persist in the neurons of 
the brain which may never actually operate as motor tenden- 
cies or memory images. But the retention effects of weaker 
excitations are probably effaced in the course of time by other 
more powerful impulses. 

4. Metabolic Variation. — In addition to the retention ef- 
fect another sort of change occurs in the neurons. This is due 
to variations in the metabolic condition of the nerve substance 
itself. Some of the receptors and effectors are highly suscep- 
tible to metabolic change. The rods and cones of the retina 
are greatly fatigued by prolonged stimulation with bright 
light. The muscles of the arm are fatigued by prolonged ac- 
tivity. These metabolic changes in the terminal organs fre- 
quently play an important part in the mental life of man. 

Recent physiological investigation indicates that the nerve 
substance also undergoes some katabolism as the result of 
the conduction of nervous impulses, but that this metabolism 
is very slight. On the other hand, the substance at the 
synapses appears quite susceptible to metabolic change. The 
metabolic condition of the synapses determines the ease of 
discharge of a nerve impulse from one neuron to the next. If 
a synapse is fatigued, the discharge is impeded and may be 
entirely prevented. If a neuron has several collaterals be- 
sides the main axon terminal, the impulse may be inhibited 
from passing over the synapses at the end of some of these on 
account of their highly katabolic condition and will be shunted 
into others which afford lines of lesser resistance. [Fig. 21.1 

This variation of metabolic condition at the synapses ac- 
counts in part for the fact that the same initial excitation will 
lead at one time to one action, at another time to another. 
When a friend invites you to go walking with him, sometimes 
you accept, at other times you decline. The variation in your 




METABOLIC VARIATION 67 

response is due to the different paths which the nerve cur- 
rent takes on the various occasions and to the specific brain 
areas which it traverses. 

In prolonged thinking a continuous process of katabohsm 
takes place in the brain. It results in fatigue and finally in 
exhaustion. The period 
of sleep serves to re- 
store the metabolic equi- 
librium. If we take as 
standard of measurement 

the average metabolic ^^]y ~" *^^^ ^^^ 

condition of the synapses, c 2 

any change toward great- Fig. 21. — Alternative Nerve Paths 

er katabolism in a given impulse from receptor Rl, when it reaches center 

CI, may either pass directly to effector El, or be 
synapse means the check- shunted to center C2 and thence to effector E2; it may 

; , , l„4-„ :„l,:u^ also he distributed to both paths. Similarly for R2. 

mg or complete mhlbl- a, a = association neurons. [From Herrick.J 

tion of discharge through 

that synapse, and any change toward anabolism means fa- 
cilitation of discharge in that direction. These are im- 
portant factors in the formation of habits (ch. vii) . 

The metabolic condition of the synapses is one factor in 
determining the course of nerve impulses; it is distinct from 
the retention effect in nerve substance. The former effect 
(fatigue and its opposite) is more transitory than the latter. 

5. Summation of Impulses. — The nature of the nerve im- 
pulse is altered when several impulses from different neurons 
unite together in a single higher neuron. In the central sys- 
tem the dendrites of a neuron are so spread out that they are 
able to receive impulses from several separate neurons. 

We have noticed that the fibers of the sensory neurons 
extend side by side without contact, somewhat like the sepa- 
rate wires in an underground telephone cable. But when the 
impulses which travel over them reach the brain the central 
neurons collect together impulses from many of these separate 
paths. This is illustrated in some of our experiences. When 



68 



PHYSIOLOGY OF THE NEURON 



we perceive a human face as a single object, or observe a table 
or an orange or any other object, the integrated perception 
is apparently due to the gathering together of many impulses 
which were received by separate rods and cones in the retina 
and transmitted separately to the visual center. When we 
perceive an orange as heavy, smooth, yellow, and sweet- 
scented, separate impulses from certain muscle receptors, 
touch corpuscles, retinal cones, and olfactory spindles are 





Fig. 22. — Summation of 
Nerve Impulses 

Simultaneous impulses from two 
receptors Rl, R2, combine in center 
C, and the summated impulse trav- 
els to effector E. FCP ■= final com- 
mon path. [From Herrick.] 



Fig. 23. — Distribution of 
THE Nerve Impulse 

Impulse from receptor R branches 
at center C and is distributed over 
paths leading to two effectors El, 
E2. [From Herrick.) 



united in the same way. The result in each case is a complex 
impulse due to the combination of separate sensory impulses. 
This combination is called summation or fusion. [Fig. 22.] 

The motor impulses which produce compound reflexes are 
due to summation of sensory impulses with impulses from 
lower centers. In instinctive and intelligent activity the 
complex motor impulses are due to summation of sensory 
impulses which takes place in the centers of the brain. 

6. Distribution of Impulses. — The collaterals of the sen- 
sory and central neurons serve to disperse nerve impulses as 
well as to gather them together. Most of these neurons - 
branch out and are provided with several end-synapses. As 
a result of retention and metabolic variation, part of the im- 
pulse may pass over into one higher neuron and part into 
another. [Fig. 23, cf. Fig. 21.] The effect is to arouse several ' 
central or motor activities at once. This gives rise to com- 



DISTRIBUTION OF IMPULSES 69 

plex central and motor processes. This property of neural 
activity is called distribution of impulses. 

When we perform any complicated act, such as guiding an 
automobile or talking, the central impulses are distributed 
into several motor paths. In running the car, our muscles 
control the steering wheel, gas, brake, and horn all at the same 
time; in talking, our lips, tongue, and diaphragm muscles are 
all simultaneously innervated. A distribution of the impulse 
occurs also in certain reflexes, such as coughing, where part 
of the impulse passes over immediately into the motor path, 
producing the reflex, while part is carried along to the brain, 
producing a sensation of tickling in the throat. 

Retention and metabolic variation may result in alterna- 
tion of paths, whereby the whole impulse is discharged at one 
time into one channel, at another time into another. In such 
cases no distribution occurs. 

7. Modification of Impulses. — In addition to the six 
operations of nerve just examined, we may reckon as a distinct 
factor the modifying influence of one impulse upon another 
when the two are summated. In like manner, when an im- 
pulse passes into a neuron which has been affected by pre- 
vious impulses, the retention trace apparently modifies its 
mode. 

In physics, when two forces of the same sort (such as sound 
waves) come together, they modify each other; if the two are 
in opposite phases they may neutralize each other in part, 
producing a less intense sound. To what extent such modi- 
fication occurs in nerve impulses is not yet known. The evi- 
dence from subjective experience leads us to believe that it is 
quite general. A number of experiences of a similar sort 
combine to produce a ' generic image,' in which the common 
features are prominent and dissimilar features are smoothed 
over. For example, having observed a number of horses, dif- 
fering in color, shape, and various minor characters, we ex- 
perience a general image of horse, in which the individual dif- 



70 PHYSIOLOGY OF THE NEURON 

ferences tend to disappear. Our thoughts involve an even 
greater transformation of the sensory data (ch. xv). 

It may be assumed that the transformations observed in 
conscious experiences are the subjective equivalent of modifi- 
cations of nerve impulses in the neurons of the cerebral cor- 
tex. If the retention trace in a certain neuron has become 
deeply embedded through repetition, it may greatly modify 
any new impulse which passes into that neuron. This would 
explain the fact that the optic nerve, however it be stimu- 
lated, always yields impressions of light. 

Modification is not so evidently an independent operation 
as the otl^er six forms of neural activity. It may prove to be 
merely a phase of summation. In the present state of our 
knowledge it seems best to regard it as a distinct property of 
nerve. 

Summary of Nerve Physiology. — The nerve impulse ap- 
pears to vary in two independent ways — mode and inten- 
sity. These variations are determined apparently by the 
nature of the stimuli and by the characteristic operations 
of nerve substances. We observe seven types of operations 
in nerve : 

Excitation means that the nerve is capable of receiving an 
impulse of some specific mode and intensity. 

Conduction means that when once a nerve impulse is ex- 
cited in a neuron it tends to propagate over the entire length 
of the axon and collaterals, and to discharge into the further- 
lying synapses. 

Retention means that the mode of a nerve impulse tends to 
leave a ' trace ' or ' set ' of some sort in the nerve substance, 
whereby any succeeding impulse will tend to conform more or 
less to this same mode. 

Metabolic variation means that the nerve substance and 
the interneural substance at the synapses are subject to kata-^ 
bolic and anabolic changes, the former being due to activity, 
the latter to rest. Katabolism checks or inhibits discharge 



SUMMARY OF NERVE PHYSIOLOGY 71 

through the given synapse; anabolism facilitates the passage 
of the impulse. 

Sumviation means that impulses from two or more neurons 
may be gathered into one single neuron further along in the 
chain, which produces a complex impulse in the latter neuron. 
The effect occurs sometimes in the motor neurons, but its 
most important operation is in the brain centers. 

Distribution means that a single impulse in one neuron may 
pass simultaneously to two or more neurons further along in 
the chain. This results in complex motor activity. 

Modification means that the mode of an impulse is altered 
when it combines with another impulse, or that it may be al- 
tered by the retention trace in the neurons through which it 
passes. 

COLLATEEAL READING: , 

Herrick, C. J., Introduction to Neurology, chs. 6, 20. 

Ladd and Woodworth, Physiological Psychology, Part I, chs. 6, 11. 

Dearborn, G. V. N., What a Student of Elementary Psychology should be 

Taught concerning the Function of the Nervous System, J. of Psychol. 

and Neurol., 1914, 2i, 35-44. 
Halliburton, W. D., Handbook of Physiology, chs. 14, 16. 
Bayliss, W. M., Principles of General Physiology, ch. 15. 
Starling, E. H., Principles of Human Physiology, ch. 6. 
Harris, D. F., Nerves, ch. 2. 
Lucas, K., Conduction of the Nervous Impulse. 
Verworn, M., Irritability, ch. 6. 
Tashiro, S., A Chemical Sign of Life, ch. 6. 
Semon, R., Die Mneme. 

Practical Exercises: 

Examine one of your earliest definite childhood recollections: (a) What de- 
tails are vivid, what are vague. (6) Your age at the time, and how you 
fix the date, (c) Whether any details were possibly supplied by some 
one's narrating the occurrence or by your "reading them in" more re- 
cently, (d) Any assignable reason why this recollection should have 
persisted. 

When sleepy or mentally fatigued, try to work out some diflBcult problem; 
analyze the experience. 

Describe the "feeling of familiarity" which accompanies your experience 
of seeing an old friend or a well-known building. 



CHAPTER V 
STIMULATION, ADJUSTMENT, AND RESPONSE 

The Nervous Arc and its Segments. — The seven proper- 
ties of nerve just mentioned belong to all neurons. But the 
operation of any single neuron means nothing for mental life 
apart from its connection with other neurons and with the 
terminal organs. The specific function of the nervous system 
is to mediate between the organism and its environment. 
This is accomplished by the activity of the nervous arc, con- 
sisting of three segments. 

Certain effects are produced in the afferent neurons (sensory 
segment) by conditions in the world outside or by conditions 
within the body; as a result, the efferent neurons (motor seg- 
ment) arouse certain activities in the effectors, which modify 
the environment. These two sorts of effects are coordinated 
by the connecting neurons (central segment), in such a way 
that the movements and glandular activity of the creature 
at any given time are more or less appropriate (adapted) to 
the situation which confronts him. When food is available 
and he is hungry he acts so as to secure the food. When 
danger appears he runs away. 

The sensory segment of the nervous arc consists of one or 
more neurons placed end to end, so as to form a pathway 
which connects a receptor organ with some center in the 
spinal cord or brain. The central segment of the arc consists 
of one or more neurons forming a pathway which connects the 
central (inner) end of the sensory path with the inner end of 
a motor path. The motor segment is a pathway which starts 
at a center in the brain or cord and leads to some muscle or 
gland. If we take into account the receptor and effector or- 
gans, the circuit consists of five parts: receptor, sensory (or 



THE NERVOUS ARC 73 

initial) path, central (or internuncial) path, motor (or end) 
path, effector organ. 

As a matter of fact the central connections are so intricate 
that it is impossible to distinguish any given nervous arc 
from certain others. When we are watching a foot-ball game, 
the optic nerve receives a steady stream of visual stimuli. 
In such cases the central connection from the optic nerve may 
lead sometimes into one motor path, when we clap our hands; 
at other times into quite a different motor path, when we 
shout and yell; or into still a third path, when we jump up 
and down in excitement. But these same motor paths for 
hand-clapping, shouting, or jumping, may in other cases be 
joined up with the auditory nerve; we may respond by any 
one of these modes of expression when we listen to an exciting 
story. ^ The motor section is often called the ' common end- 
path ' of the impulse. The sensory section is just as truly 
a common initial-path. 

The simplest arcs of all terminate in the spinal cord. In 
these the central part may be entirely lacking. The nerve 
impulse goes up the sensory path to the cord, and thence 
passes directly over into the motor path and so out to the 
effector. A simple arc of this sort is called a spinal circuit, 
and the nervous action is called a spinal reflex. Most circuits 
lead up the spinal cord into the brain, or if they start in the 
head they form a brain circuit. The circuits which pass 
through the brain are of various degrees of complexity. In 
the case of a well- organized habit the path is probably com- 
paratively simple. In planning how to build a house or write 
a book or organize a business, some of the circuits may in- 
clude long chains of neurons in the central portion of the 
arc. 

Operation of Each Segment. — The circuit of neural ac- 
tivity which operates in any nervous arc or in a complex sys- 

^ Fig. 21 on p. 67 illustrates these alternative connections in a sche 
matic way. 



74 STIMULATION 

tern of arcs is known as behavior; but every instance of be- 
havior includes three separate stages, which correspond to the 
parts of the nervous arc. In discussing the operations of the 
three segments of the arc, it will be convenient to treat the 
central part last. The three operations are called Stimulation, 
Response, and Adjustment. (1) Stimulation is the effect of 
external or bodily conditions upon the sensory part of the 
nervous arc. (2) Response is the effect of the motor portions 
of the arc upon the effectors and upon the environment. 
(3) Adjustment includes (a) the collection of sensory impulses 
at the centers and (6) distribution of out-going impulses from 
the centers into appropriate motor channels. The former is 
called Integration, the latter Coordination. 

1. Stimulation 

Nature of Stimulation. — So far as we know, a nerve im- 
pulse never starts within a neuron except as the result of ex- 
citation from outside that neuron. Sensory neurons receive 
impulses from the receptors or from other sensory neurons. 
Motor and central neurons (save perhaps in exceptional cases) 
receive all their impulses from sensory neurons or from other 
motor or central neurons. They are not directly excited by 
activities in the other body tissues. 

Thus the origin of every ordinary nerve impulse may be 
traced directly or indirectly to some force outside the nervous 
system acting upon the peripheral endings of sensory neurons. 
This initial excitation is called stimulation. Not all stimuli 
are due to forces outside of the body. Activity of the diges- 
tive and other internal organs stimulates the receptors and 
sensory nerves which lie in these regions; and muscular ac- 
tivity stimulates receptors and sensory nerves connected with 
the muscles, tendons, and joints. 

Most nerve impulses are aroused by activity in a receptor 
organ; but certain pain nerves terminate peripherally in the 
epithelial tissues and have no special receptors; activity in 



NATURE OF STIMULATION 75 

these tissues stimulates the pain nerves directly. (These are 
called /ree nerve endings.) 

We may state, then, as a general law, that all neural ac- 
tivity originates outside of the nervous system through the 
process of excitation. The original excitation of a sensory 
neuron by a non-neural force is called stimulation, and the 
force which causes the process of stimulation is termed a 
stimulus. 

Role of the Stimulus. — Stimuli vary in intensity, mode 
(quality), extent, and duration. But the two latter variations 
affect the impulse in a different way from the first two. (1) An 
extended stimulus does not alter the nature of the impulse in 
any single sensory neuron, but it may stimulate a great num- 
ber of receptors and sensory neurons, and the resulting im- 
pulses may be summated at the centers. (2) If a stimulus 
continues for some time, the duration affects the impulse 
in much the same way that previous stimuli affect a later 
stimulus. We may therefore treat an enduring stimulus as 
if it were made up of a series of momentary stimuli, each with- 
out appreciable duration. So far as the effect of stimulation 
upon any single sensory impulse is concerned, extent and dura- 
tion may be ruled out. These variations affect the central 
and motor operations only. The only variations which we 
need consider in connection with stimulation are intensity 
and mode. We have already noticed these factors in discuss- 
ing the nerve impulse (ch. iv) . Differences of intensity among 
stimuli produce differences of intensity in the impulses, and 
modal differences among stimuli lead to modal differences 
in the impulses. 

(a) Mode : Each type of receptor is capable of being stimu- 
lated by a specific kind of force, and its capacity is limited 
to a certain range of modes of that force. Thus the visual re- 
ceptors in the eye are ordinarily affected only by light waves, 
and only by a certain range among these. In certain cases 
a different kind of force than the usual stimulus produces an 



76 STIMULATION 

effect upon a receptor; the eye may be stimulated visually by 
rubbing or pressing the eyeball. These unusual modes are 
called inadequate stimuli, while the normal kinds are termed 
adequate stimuli. 

Corresponding to the different kinds of stimulation in the 
various types of receptor and to different modes of stimula- 
tion in receptors of the same type, the nerve impulse assumes 
different forms, or modes, as described in chapter iv.^ Where 
stimuli are so different that they act upon different kinds of 
receptors the resulting sensory impulses are quite hetero- 
geneous. They are centrally observed as sensations of touch, 
sight, hearing, etc. The modal differences within the range 
of the same receptor may be illustrated by the central im- 
pulses (sensations) due to red, green, and other visual stimuli. 

So far as we know, any sensory nerve might readily trans- 
mit any other kind of impulse besides its own, if connected 
with appropriate receptors. The optic nerve, for instance, 
might transmit olfactory impulses if connected with the re- 
ceptors in the nose. As a matter of fact, however, the optic 
nerve has been connected from the outset with the retinal 
rods and cones, and practically all the impulses which it has 
transmitted have been of the visual type. These impulses 
have produced a retention effect, probably in the nervous 
tissue of the optic nerve, so that an occasional inadequate 
stimulus, such as a blow on the head or an electric current, 
would tend to take the same form. We may assume, then, 
that each set of sensory nerves carries impulses of one par- 
ticular kind, for the simple reason that it is connected with 
certain receptors, and that these receptors are normally af- 
fected by only one class of stimuli. 

The effect of stimulation when it reaches the brain center, 
and especially the cortex, is of peculiar interest to psychology, 
because it enables us to apply the method of self-observation 
to the receptive process. The central effect of stimulation, 

1 See p. 58. 



ROLE OF THE STIMULUS 77 

observed in ourselves, is called a sensation. The mode of a 
sensation is related in a definite way to the mode of the 
stimulus. 

Since no means have yet been devised for measuring the 
nerve impulse in the brain directly, we have to rely entirely 
on the results of self-observation. We observe and report 
our sensations, which correspond to the physiological processes 
in the brain. 

Let m = the mode of stimulation, /j. = the mode of nerve 
impulse at the center, and M = the mode (or quality) of 
the observed sensation. Then 

fji. = e (m), or M = ^ (m), 

since M represents /* as it appears to the observer himself. 
In these equations is not necessarily a quantitative func- 
tion, but signifies that m changes concomitantly with /^ or M. 
For example, if m is a green light-wave, it produces a certain 
mode of effect in the brain center to which corresponds the 
sensation of green. If the stimulus be altered to a red light- 
wave, there is a corresponding change in the sensation. 
The human organism is capable of being affected by a great 
many different modes of stimuli. The qualitative differences of 
sensation to which these give rise will be discussed in chapters 
ix and x. 

(6) Intensity: Experimental investigation within the 
past sixty years has brought to light some very definite mathe- 
matical relations between the intensity of stimulation and 
the intensity of the resulting impulse. These results have 
been obtained by measuring the intensity of stimuli in phys- 
ical terms and comparing this with the central effect as 
reported by self -observation. Two stimuli differing in inten- 
sity are applied to the same receptor and the resulting sensa- 
tions are observed and compared by the individual experi- 
mented upon. E. H. Weber, G. T. Fechner, and many 
later investigators applied this method to nearly every kind 



78 STIMULATION 

of stimulus. It is found that the intensity of the stimu- 
lus and the intensity of the resulting central impulse (ob- 
served as sensation) are related generally according to the 
logarithmic function. 

Let i = intensity of stimulus, t = intensity of nerve im- 
pulse at the center, and I = intensity of sensation. Then 

c = (f> (i), or I = </) (i), 

since I = t as it appears to the subject. But according to 
the experimental results, known as Weber's Law, 4> repre- 
sents the logarithmic function; so that the equation reduces to 

I = k log. i, 

where k denotes a constant which is the same for any given 
receptor, but differs for different kinds of receptors. For 
example, in hearing, the constant is f ; that is, equal increases 
in observed intensities of sound occur when the stimuli increase 
in the ratio 1, |, ^9^, f4, etc.^ 

Role of the Receptor. — The process of stimulation and 
the nature of the sensory impulse depend quite as much upon 
the make-up of the receptor as upon the stimulus itself. The 
constitution of the receptor determines to some extent (1) the 
mode and (2) the intensity of the sensory impulse; (3) the 
metabolic condition of the receptor alters the intensity still 
further. 

(1) The mode of the impulse and quality of sensation are 
determined by the process which goes on in the receptor. It 
is fruitless to speculate whether it would be possible to develop 
receptors which would enable us to see sounds or hear light. 
But within the range of a given receptor there are individual 
variations. The same light- wave stimulus which to one per- 
son appears green, to another looks yellow, to another gray. 
These differences are due to the constitution of the receptor; 
the first is called a ' normal eye,' the others are different types 

^ See ch. xii. 



R6LE of the receptor 79 

of color-blind eye (ch. ix). We receive the sensations red, 
green, bitter, sweet, etc., not only because each receptor is 
capable of being affected by certain stimuli, but because the 
physiological process set up in the receptor by each of these 
stimuli is of a certain definite mode. 

Furthermore the efficacy of the stimulus is limited to the 
range of the receptor's capacity. Ultra-violet light- waves, for 
instance, produce no effect whatever in the rods or cones of 
the eye; sound waves and odor stimuli do not affect the eye 
though they do affect other receptors. The receptor does not 
start an impulse unless it is stimulated; but it determines 
whether or not a given stimulus shall work, and it also deter- 
mines the precise mode of the impulse for such stimuli as 
do affect it. 

(2) The make-up of the receptor is a factor in determining 
the intensity of the impulse also. A very feeble physical 
stimulus may produce no effect whatever in the receptor, and 
the actual intensity of any sensory impulse depends upon the 
intensity of the process set up in the receptor. Further, a 
receptor is affected only up to the limit of its capacity. If 
the physical stimulus is so intense that it exceeds the capacity 
of the receptor the sensory impulse is not increased beyond 
this limit. Very intense light blinds us, and intense sound 
vibrations destroy the ear-drum. The rate of increase of 
the impulse is also partly determined by the receptor. The 
constant k in the Weber formula varies for different types 
of receptor. 

(3) The metabolic condition of the receptor varies from time 
to time, and this also alters the nature of the impulse. If a 
receptor becomes fatigued through constant use, its physio- 
logical efficiency is impaired. Thus the taste receptor be- 
comes ' blunted ' when the same sort of stimulus is applied 
repeatedly, so that a sweet substance no longer tastes so sweet. 

In sight the fatigue factor appears to alter the mode of 
impulse as well as its intensity. When we look steadily at a 



80 STIMULATION 

red spot for a long time and then turn the eye to a white sur- 
face, the part of the retina previously stimulated by the red 
now appears greenish instead of white.. This, however, is 
really an intensity phenomenon ; for the ' white retinal activ- 
ity ' is a compound process of which one component has been 
blunted by long-continued stimulation. In general, then, the 
metabolic condition of the receptor alters the intensity of the 
impulse as determined by the original stimulus. A katabolic 
state decreases the intensity of the impulse, while a highly 
anabolic state serves to increase it. 

Role of the Sensory Neurons. — Finally, the effect of stim- 
ulation is dependent to some extent upon the state of the 
sensory neurons. The nature of the sensory impulse as de- 
termined by the stimulus and by the receptor may be altered 
before it reaches the center, either (a) by the retention effect 
in the nerves or (6) by the metabolic condition of the inter- 
mediate synapses. The retention trace of the neurons due 
to previous stimulation may alter the mode of the impulse, 
while the metabolic condition of the synapses may alter its 
quantitative value. Thus a 'familiar ' color, taste, etc., is ob- 
served to have a slightly different quality from a new experi- 
ence; this is due to the retention trace. A loud sound may not 
be observed at all if the communicating pathway is obstructed 
at the synapses ; this occurs in conditions of ' inattention. ' We 
shall examine these factors more closely later (ch. viii). 

General Laws of Stimulation. — The various factors con- 
cerned in stimulation may be summed up in the following 
laws: 

(1) The nature of the sensory impulse depends upon the 
nature of the stimulus; this involves two independent vari- 
ables: (a) the mode of the impulse (and quality of sensation) 
depends primarily upon the mode of the stimulus; (6) the 
intensity of the impulse (and sensation) depends upon the 
intensity of the stimulus. 

(2) The nature of the sensory impulse depends also upon 



GENERAL LAWS 81 

the receptor. The actual mode and intensity of an initial 
sensory impulse is determined by the nature and capacity 
of the receptor and by its metabolic condition at the time of 
stimulation. 

(3) The character of the sensory impulse when it reaches 
the center depends also upon the retention trace in the inter- 
mediate neurons and upon the metabolic condition of the 
intermediate synapses. Retention alters the mode of the 
central impulse and the quality of sensation, while the meta- 
bolic state of the synapses affects the quantitative value of 
the central impulse. 

2. Response 

Nature of Response. — Every nerve impulse, unless dissi- 
pated by resistance along its pathway or transformed into 
potential energy, finally discharges through the motor segment 
of the arc into the effectors and produces physiological ac- 
tivity in these. The activity of the effectors, together with 
the grosser movements and other changes which result from 
this activity, is termed the response. It is so called because it 
is regarded as the creature's ' answer ' to the problem which 
the environment puts up to him through stimulation. Re- 
sponse is the motor effect of whatever sort brought about by 
nerve activity. It includes (a) muscular contraction and 
(6) glandular secretion, with all the bodily movements or 
transfer of substance within the body and all environmental 
changes which result from these processes. 

a. Muscular Response. — Muscular activity is the most 
important type of response in man. Many separate neurons 
terminate in each muscle. Ordinarily the motor impulse 
affects all these separate neurons at once, with the result 
that energy is imparted to the entire muscle and it is thrown 
into a condition of physiological activity. This activity pro- 
duces contraction of the muscular tissue, which causes it to 
. shorten lengthwise and thicken in diameter. [See Fig. 20.] 



82 RESPONSE 

The process of contraction is more speedy according as the 
intensity of excitation is greater. The duration of the state 
of contraction depends on the duration of the impulse. When 
the motor impulse ceases the muscle relaxes and returns 
to its original state. 

The energy of the muscular response is very great com- 
pared with that of the nerve impulse which excites it. The 
nerve impulse serves merely to ' touch off ' the activity in the 
muscle, somewhat as pulling the trigger of a rifle releases the 
energy stored in the cartridge. 

Mode of Impulse. — The mode of the nerve impulse has no 
apparent effect on the character of the response. The only 
exception to this is (possibly) in the case of inhibitory motor 
impulses. There are some indications that the motor nerve is 
capable of transmitting a special type of nerve impulse which 
has the effect of checking or neutralizing the contraction of 
the muscle; but the nature of inhibitory impulses is at pres- 
ent uncertain. Most muscles occur in pairs, called antag- 
onists, one of which serves to move the member in one direc- 
tion, the other in the opposite direction; as when we bend and 
straighten the arm. The so-called inhibitory impulse is pos- 
sibly only a shunting of the motor impulse from a given 
muscle to its antagonist. 

While the mode of the nerve impulse has no effect in mod- 
ifying muscular contraction, it does have an important bear- 
ing upon the type of response. The mode of the central nerve 
impulse probably determines to some extent which motor 
path out of all possible connections will be affected. If the 
central nerve impulse has a certain mode, it is able to permeate 
certain motor synapses; if it has a slightly different mode it 
passes into other motor paths. For example, when I recall 
some annoying occurrence the central process may start a 
motor impulse which results in my clenching the fist; whereas 
a similar thought, but with a different tinge, may result in 
scowling, kicking, or a flow of vituperative language. This, 



MODE OF IMPULSE 83 

selection of motor paths probably depends upon the retention 
trace in certain motor nerves being similar to the mode of the 
present central nerve impulse. The path once determined, 
however, the mode of the impulse has no apparent effect on 
the muscular contraction. 

Other Factors determining Response. — The final effect 
of the motor impulse depends also upon the metabolic condi- 
tion of the motor synapses and of the muscular tissue. A 
muscle ' fatigued ' through constant use of the same path 
contracts more slowly than one which is ' rested ' and re- 
stored by anabolism. 

The rate and amount of muscular contraction is also de- 
pendent upon the amount of resistance to the movement. If 
we lift a heavy weight the contraction proceeds more slowly 
or is more limited in extent than if we merely raise the arm 
itself. Normally, however, the rate of contraction is regu- 
lated by means of a secondary arc. When we begin a move- 
ment the kinesthetic receptors in the muscles report the state 
of contraction at every instant. If the arm muscles move 
freely their receptors are slightly stimulated; while if the mus- 
cular activity meets with resistance the kinesthetic stimu- 
lation is greater. This secondary stimulation results in a 
secondary motor impulse which supplements the original 
impulse and regulates the response. If we start to lift a 
heavy object which appears to be light, the initial motor im- 
pulse carries too little energy and the movement is not ac- 
complished; but kinesthetic stimuli report the failure, and 
this secondary excitation starts a more intense motor impulse 
to the appropriate muscles. In the opposite case, the motor 
impulse may be ' toned down ' by the secondary excitation. 

The significance of the muscular type of response consists 
not in the muscular contraction as such, but in the bodily 
movements which it brings about. Responses include va- 
rious movements of the arms and legs, head, trunk, face, vocal 
apparatus, etc. The combination of muscular activities which 



84 RESPONSE 

result in any specific adjusted movement (such as rowing, 
walking, uttering a sentence) depends, however, far more 
upon the central coordinating activity than upon the motor 
discharge, so that we may leave this phrase of response for 
later discussion. 

b. Glandular Response. — Glandular activity plays a far 
less important role in mental life than muscular activity; yet 
in many cases it forms an integral part of the response. 
Psychologists have only recently begun to appreciate the 
extent to which the glands are concerned in behavior. 

Certain efferent paths terminate in the glands. When these 
' motor ' neurons are excited by central activity the impulse 
energizes the glands and causes them to become active. This 
activity results in their secreting certain chemical com- 
pounds. For example, certain motor impulses affect our 
lachrymal glands and cause us to shed tears. The original 
stimulus may be either a bit of cinder in the eye, or a blow on 
the back, or a message announcing the death of a near friend. 

One and the same sort of glandular activity may be com- 
bined with various modes of muscular activity in different 
responses. Weeping, for instance, may accompany ' rage ' 
movements as well as ' defense ' movements. Glandular activ- 
ity which results in the secretion of saliva, urine, sweat, etc., 
forms part of the motor response when it is due to specific 
stimuli, but not when it is connected with the vital functions 
of nutrition and regulation. In the latter case it falls out- 
side the limits of psychology. 

General Laws of Response. — (1) The speed of muscular 
contraction depends primarily upon the intensity of the motor 
impulse. 

(2) It depends also upon the metabolic condition of the 
motor synapses and upon the resistance of a weighted muscle. 

(3) The motor impulse may be regulated by a secondary arc 
whose activity is stimulated by the kinesthetic receptors. 

(4) Similarity between the mode of a central impulse and 



GENERAL LAWS 85 

the retention trace in the motor section of the arc may deter- 
mine which path of several alternatives the motor impulse 
will take, but otherwise the mode of the motor impulse has no 
effect upon the type of response. 

(5) Response includes the gross bodily movements which 
result from muscular activity as well as the muscular con- 
traction itself; it includes also glandular activity so far as this 
is regulated by impulses from the cerebrospinal centers. Any 
change in the environment brought about by these muscular 
or glandular activities is part of the response. 

(6) Coordinated responses, whether muscular, glandular, or 
mixed, depend upon the adjustive activity of the central part 
of the arc. 

3. Adjustment (Integration and Coordination) 

Nature of Adjustment. — The function of the central por- 
tion of the nervous arc is not merely to carry each separate 
sensory impulse over into a specific motor path. If this were 
its only role, the central system would scarcely deserve special 
notice; it would simply furnish certain additional links to the 
chain of sensory neurons, each of which receives the impulse 
from the preceding neuron and passes it on in turn to the next. 
In simple reflex arcs, like those concerned in sneezing and 
iris contraction, the central part of the arc actually does this : 
it merely transfers from the sensory to the motor path. Here 
the connecting neuron may be considered as part of the sen- 
sory segment, or as part of the motor segment. It has no 
special role of its own. 

In all but the simplest arcs, however, the central neurons 
have several alternative connections. Some of these col- 
lect impulses from a number of separate sensory paths and 
combine them into one complex impulse; others distribute an 
impulse into several separate central and motor pathways, 
and thereby multiply its effects. Thus a response of the 
higher sort is usually not a simple outcome from a single stim' 



86 ADJUSTMENT 

ulus; a given stimulus may produce various kinds of response 
if its impulse reaches the higher centers. The central section 
in any ' higher ' arc is connected with many sensory and many 
motor segments. It receives a ' system ' of sensory impulses 
and sends out a ' system ' of motor impulses. The combina- 
tion (summation) of sensory impulses which occurs in the 
central part of the arc is called integration, and the capacity 
of the centers to distribute cooperating motor impulses is 
called coordination. Integration is illustrated in the percep- 
tion of a book or other object as a single experience comprising 
various distinctive parts; coordination is illustrated by the 
simultaneous and successive muscular contractions which 
occur when we take hold of the book and lift it. The entire 
process is termed adjustment. It involves a complex, coordi- 
nated response to complex, integrated stimulation. 

All the fundamental operations of nerve occur in the ad- 
justive function of the central system. Summation is a prom- 
inent factor in integration, and distribution is the distinctive 
feature of coordination. Retention traces, variations in the 
metabolic condition of the central synapses, and modijfica- 
tion, all affect the path of the impulse through the central 
region and assist in determining the process of adjustment. 

Role of Retention and Modification. — The retention trace 
due to former impulses persists to a greater degree in the cen- 
tral neurons than in the sensory, since the sensory neurons 
are stimulated by impulses of many different modes. In the 
central system the neurons are apparently ' sorted out ' some- 
what according to the modes of their retention traces. 

When any central neuron has received a certain mode of 
impulse it retains the effect of that mode. Thereafter it re- 
ceives similar impulses more readily, and becomes less capable 
of receiving different impulses. If a somewhat dissimilar im- 
pulse reaches it, it may pass across the synapse and be modi- 
fied by the retention trace, at the same time modifying the 
trace in that neuron. The extent of the modification depends 



RETENTION AND MODIFICATION 87 

upon the intensity of the new impulse and the permanency 
of the trace. 

If the new impulse is very intense it will be only slightly 
modified by the trace but will modify the trace very much. 
An illustration of this effect is observed when we fi.rst see a 
black swan. The perception is slightly modified by our pre- 
vious experiences of white swans, while our general notion of 
swan (the result of many retention effects) is greatly modified 
by the new experience. If the new impulse is weak, the cen- 
tral impulse may be quite modified and conform to the mode 
of the retained trace, while the trace itself is not much altered. 
This occurs when_ the sight of a printed word suggests its 
auditory equivalent. If the new impulse is very similar to the 
trace left by former impulses, neither mode is much modified; 
as when we see a familiar scene. 

On the motor side, central retention leads to the discharge 
of the impulse along the same paths as on previous occasions. 
This is illustrated by any well-formed habit, as when one 
writes his own name, or turns in at a familiar gate during a 
walk. The retention factor is the basis of all memorization 
and motor habits. It is owing to retention that every musi- 
cian has his own peculiar ' touch, ' that each of us pronounces 
words in his own way, etc. 

Role of Metabolic Condition. — The metabolic condition 
of the central synapses affects the intensity of the incoming 
impulse. (The retention trace affects the mode.) The effect 
of metabolic variation is observed in the ' unevenness ' which 
characterizes perception. Certain features of an object are 
prominent, other details are in the " margin of consciousness." 
The " fluctuation of attention " is another instance of sensory 
change due to central metabolism. 

On the motor side, the metabolic condition determines to 
some extent which of two alternative motor paths shall receive 
the outgoing impulse. If one pathway has been in constant 
use, its synaptic connections become ' fatigued ' and for a 



88 ADJUSTMENT , 

time offer greater resistance to the passage of impulses; as a 
result the impulse passes out over some other synapse which 
offers less resistance, and is thereby shunted into another 
path. This is illustrated by the normal variations of our 
motor activities; we frequently shift from one kind of work 
to another. 

Laws of Adjustment. — Our results so far may be summed 
up in the following laws : 

(1) The simplest operation of the central part of the arc is 
to convey a nerve impulse from a sensory path to a motor path 
{^conduction). 

(2) The higher central neurons serve to integrate several 
sensory impulses into one complex impulse; this is accom- 
plished by means of their collateral branches; it involves the 
summation of impulses. 

(3) The higher central neurons also coordinate motor im- 
pulses by sending out several cooperating impulses at once. 
This involves the distribution of an impulse through several 
branches. 

(4) The central activity depends not merely upon the mode 
and intensity of the impulses which it receives, but also upon 
the retention trace left by previous impulses in the central 
neurons themselves, and upon the metabolic condition of the 
central synapses. Retention alters the mode of the received 
impulse, metabolic conditions alter its intensity. Both are 
factors in determining the path of motor discharge. 

Significance of the Central System. — The more closely 
the workings of the nervous mechanism are examined, the 
more evident does it become that the central section of the arc 
is its most essential part. It is by means of central processes 
that we receive and ' grasp ' as a whole a complex situation 
which confronts us in the environment; and it is by means of 
these same processes that our movements, instead of being 
detached reflexes, become adapted responses ' appropriate ' 
to the total situation. Whether we shall reach out and catch 



SIGNIFICANCE OF CENTRAL SYSTEM 89 

an approaching ball, or shall dodge it, depends upon the in- 
tegrative action of the central system; and the complex group 
of muscular contractions which we perform in either case are 
determined by the coordinating action of the same system. 

We should not undervalue the sensory and motor functions. 
The central system acts upon the sensory data which it re- 
ceives; its efficacy is due in large measure to the complexity 
of the stimuli and to the differentiation of the receptors. And 
since the centrally adjusted impulse acts through the motor 
paths and effector organs, the suitability of the response de- 
pends upon the presence of numerous muscles advantageously 
placed and in good working order. Granting all this, we must 
stiU recognize that the central system is the prime factor in 
adjusting the response to the situation. — 

So remarkable are the fine adjustments which the central 
system carries out, that many investigators refuse to believe 
that the brain as a mere nerve mechanism is capable of per- 
forming them. Thus we have the ' interaction ' theory of 
adjustment, which holds that the receptive data are handed 
over to a mental personality which is distinct from the brain 
— which ' intuits ' the situation and ' decides ' upon a course 
of action, and then energizes the appropriate motor centers. 
While this view is quite tenable, it offers difficulties of its own, 
and in fact only removes the explanation from processes 
with which we are more or less familiar and carries it further 
into the realm of the unknown.^ 

Methods of Investigating Adjustment. — The real prob- 
lem in explaining the process of adjustment is to show how the 
integration and coordiiKCtion which we observe in organisms 
is actually brought about, and how it happens that the total 
response is appropriate to the stimulus-situation. 

No means have as yet been devised for observing the opera- 
tion of nerve activity in the living brain; and if the central 

^ See Appendix, "Subjective and Objective Phenomena," p. 413; "Con* 
scious Purpose," p. 427. 



90 ADJUSTMENT 

neurons are removed from their organic connections the whole 
process of integration and coordination disappears. In the 
present state of science the operation of adjustment can be 
studied only indirectly. 

Some light is thrown on the process by the study of brain 
structure, which enables us to trace the course of bundles of 
fibers from one part of the brain to another. These findings 
indicate what centers are actually connected. Another means 
of study, somewhat similar to this, is the so-called method of 
degeneration. If a given area in the brain be cut out or de- 
stroyed, the course of degeneration of nerve tissue follows cer- 
tain paths. Such degenerations often occur in disease, and 
many such cases have been studied in the human brain. The 
animal brain is also studied by experimental excision of brain 
centers; but the brains of all subhuman animals are so much 
simpler than the human that this method leaves much to be 
desired. 

Another indirect means of studying adjustment is through 
artificial stimulation of various parts of the brain by an elec- 
tric current. Experiments so far made by this method appear 
to show that the stimulation results in one movement or an- 
other according to the region stimulated. 

All these methods have advanced our knowledge of the ad- 
justment process considerably. But they serve only to in- 
dicate certain paths of central conduction. They do not ac- 
count for the complexity of ' integration ' and ' coordination ' 
as found in actual mental life. And this is after all our fun- 
damental problem. 

Two methods have been used in investigating this and other 
problems of psychology. (1) The study of behavior. This 
consists in working at the two ends of the nervous arc. Stim- 
uli are applied to the various receptors and the motor effect 
is noted. The stimuli may be given artificially. The animal 
or human being is placed under carefully prepared conditions, 
a measured stimulus is applied, and the resulting motor effects 



METHODS OF INVESTIGATION 91 

are measured. Or we may observe how the animal or human 
acts under natural conditions, noting the stimuli which affect 
him and the nature of his responses. (2) The study of con- 
scious experience through self-observation. Here we are 
working at the central portion of the arc, observing how the 
stimuli affect our own brain and the various stages of the 
central process culminating finally in the motor impulse. 

We shall examine the operations of mental life as indicated 
by the behavior method in the next two chapters, and then 
pass to the study of conscious experiences. 

Collateral Reading: 
Dewey, J., The Reflex Arc Concept in Psychology, Psychol. Rev., 1896, 

3, 357-370. 
Moral, J. P., Physiology of the Nervous System (trans.). Part II, ch. 2. 
Halliburton, W. D., Handbook of Physiology, chs. 49, 52. 
Forel, A., Hygiene of Nerves and Mind in Health and Disease (trans.), 

ch. 4. 
Harris, D. F., Nerves, chs. 3, 4. 
Donaldson, H. H., Growth of the Brain, chs. 13-16. 
Titchener, E. B., Experimental Psychology, Vol. II, Part II, sees. 1-6. 
Fechner, G. T., Elemente der Psychophysik. 

Sherrington, C. S., Integrative Action of the Nervous System, chs. 1-8. 
McKendrick, J. G., Principles of Physiology, ch. 7. 

Practical Exercises: 

Study (a) several cases in which you can readily perform two independent 
actions at once, and (6) several in which one act interferes with the other. 
Determine if possible a criterion for the 'cooperation' and 'interference.' 

Observe a child learning to use knife and fork; compare with your own 
movements in the same act; note and report differences in precision of 
the coordination. 

Test Weber's Law for lifted weights. Take 50 similar envelopes; weight 
each with shot, so that each is 5 grams (or | ounce) heavier than the pre- 
ceding. Lift No. 1 (10 grams) and then No. 2 (next heavier), giving judg- 
ment of " equal weight " or " second heavier." Lift No. 1 and then No. 3, 
giving judgment. In same way compare Nos. 4, 5, etc., successively 
with No. 1 as standard, till difference is just noticeable. Repeat the ex- 
periment with No. 11 as standard, comparing it with Nos. 12, 13, etc. 
Repeat with other standards (21, 31, 41), recording all the results. 
Determine the ratio between standard weight and just noticeably heavier 
weight in each case. How do these ratios compare with one another? 



CHAPTER VI 
BEHAVIOR 

Operation of the Nervous Arc; Adaptive Reaction. — In the 
two preceding chapters we have considered the special prop- 
erties of nerve which render its activity different from other 
types of cell, and the typical functions of the three segments 
of the nervous arc. But neither the characteristics of nerve 
nor the performances of the separate parts of the arc describe 
in any adequate way the activity of the nervous system when 
it operates as a whole. 

The neuro-terminal system is the mediator between the 
creature and his environment.'^ Organisms which are pro- 
vided with a nervous system react in a specific way to the 
forces exerted upon them from outside. They are not affected 
like a billiard ball struck by a cue, or like a coin when it re- 
ceives the impress of a dye. The forces which act upon the 
nervous system as stimuli lead to responsive activity on the 
part of the organism. Organic reaction is something different 
from the physical conception of reaction to an external force. 
The organism ' strikes back ' at the environment. 

We are not to interpret this striking back in an anthropo- 
morphic sense; it does not necessarily imply intelligence, con- 
sciousness, or deliberation.^ It means simply that the or- 
ganism modifies the environment and that the give-and-take 
process is somewhat different from ordinary physical action 
and reaction. The reactive response of the organism to 
stimulation is adaptive; and by this we mean that it tends to 
protect the organism from injury and to promote its life 
processes. 

Take the illustration used in chapter i. When we are out 

* See Appendix, "Thought-Transference, " p. 418. 

^ See Appendix, "Personification of Natural Phenomena," p. 433. 



OPERATION OF THE NERVOUS ARC 93 

in a gale and a gust of wind blows suddenly against us, if it is 
not so strong and sudden as to blow us over we brace ourselves 
against it. This is a typical example of organic response. The 
reaction is responsive only when the pressure acts as a stim- 
ulus and there is time for adjustment of our motor apparatus. 
The phenomenon of being ' blown over ' is not a responsive 
reaction, but a physical reaction; the wind acts upon our body 
as it might upon a vase, and we topple over. In highly organ- 
ized creatures the adjustive activity mediated by the nervous 
system serves in most cases to prevent this result, which might 
prove disastrous to the creature's existence as a living being. 

Again, when you are seated at a dinner table your receptors 
are stimulated by the sight and smell of food. Your reactive 
response is a series of complicated movements which convey 
the food to your mouth and lead to its digestion. Taken by 
itself, the action of light waves upon the retina or of odorous 
particles on the olfactory receptors is not very forceful. But 
these stimuli bring about a response in the form of coordinated 
muscular contractions and adaptive movements which serve 
to maintain your existence as a living organism. Responsive 
reactions, of which these are merely examples, tend in general 
to promote the life processes or prevent the destruction of the 
creature. This is the distinctive characteristic of the operation 
of the complete neuro-terminal arc. 

This does not mean that every single response is helpful to 
the creature. In trying to brace myself against the wind I 
may actually fall forward and receive greater injury; or in 
eating I may inadvertently introduce poison into my system. 
The notion of adaptiveness means simply that the response 
tends to be suitable to the stimulus in all ordinary situations. 
This is accounted for by the fact that unsuitable forms of 
response are more likely to cause a creature's destruction, 
and hence we assume that they are gradually weeded out 
in the course of many generations. In other words, the 
adaptiveness of response appears to rest upon natural selec- 



94 BEHAVIOR 

tion: the fittest individual and the most suitable reaction 
survive in the long run. 

Concept of Behavior. — The specific type of activity medi- 
ated by the neuro-terminal system in the manner just described 
is called behavior. Organic behavior consists of such activities 
of living creatures as are manifested in muscular contraction 
and glandular secretion (or some equivalent processes in 
lower organisms) together with the various resulting move- 
ments and physiological changes. The movements of a crea- 
ture are not behavior unless they are mediated by activity of 
the nervous arc. When a man is struck down by a blow, or 
when he is rolled over during sleep, his falling or rolling move- 
ments are not behavior. Neither are growth or the healing of 
. a wound included under the term. Behavior movements are 
such as are brought about by motor nerve impulses; and the 
latter always result from stimulation. Hence, behavior is to 
be regarded not merely as bodily movement or motor activity, 
but as the adjusted responsive effect of stimulation. It in- 
volves the operation of the entire neuro-terminal arc. 

Types of Behavior. — We might class behavior according 
to the different kinds of relationship which it brings about 
between the organism and the outer world. This would give 
such general types of behavior as feeding, defensive, aggres- 
sive, mating, parental, filial, general social, locomotor, and the 
like. But this division depends upon a rather high stage of 
nervous and mental evolution. Running away, raising our 
arms and hands, clenching the fist, and fear-expression all 
belong under defensive behavior. Yet psychologically these 
actions belong to very different types. In determining the 
response and adapting it to the situation the central nervous 
system is the important factor. The mode of central activ- 
ity in running away is quite different from what it is in 
coming to guard, and our analysis of behavior is confused if 
we class both of these types under the same heading. 

The difficulty is avoided in a classification based upon the 



TYPES OF BEHAVIOR 95 

nature of the central adjustment. On this basis human be- 
havior includes three main types: reflex action (simple 
response), instinctive behavior, and individually modified 
intelligent behavior. They are commonly called reflexes, 
instincts, and intelligence. The protozoa, or one-celled ani- 
mals, which lack a specialized nervous system, have no re- 
flexes properly speaking. But they exhibit a very similar 
form of simple response called tropism. In these species and 
among lower metazoa there are several gradations between 
simple response and instinct. In certain species of protozoa, 
such as Paramecium, the swimming activity consists in a 
combination of similar movements made by a set of cilia; 
this may be called a compound response. A similar com- 
pounding of responses occurs also in higher animals, and con- 
stitutes a grade of behavior intermediate between reflexes 
and instincts. 

In man intelligent behavior becomes differentiated into two 
distinct types, called habit and rational behavior. Habits con- 
sist of comparatively fixed modes of action, which after they 
are established resemble closely actions of the instinctive 
type; they constitute the lowest stage of intelligent behavior. 
Rational actions are more variable, and belong to a higher 
level. 

Intelligent behavior in man develops also two ' social ' 
types, communication and conduct, which are concerned with 
the relations between a man and his fellows. These varieties 
of intelligence together with reflex and instinctive behavior 
make up the general classes of mental functions mentioned 
in chapter ii. 

1. Reflex Behavior 

Reflex Action. — The reflex is the original form of behavior 
among creatures possessing a nervous system. It involves the 
operation of a single nervous arc or a number of such arcs 
acting together simultaneously. Reflexes are either simple or 



96 



REFLEX BEHAVIOR 



compound, and they are distinguished as lower or higher ac- 
cording as they involve only a lower arc or higher coordinat- 
ing centers. Usually the simple reflexes are lower and the 
compound higher. 

Simple Reflexes. — Simple reflex action is brought about by 
the operation of a simple nervous arc. In reflexes of the sim- 
plest and lowest type, the sensory nerve impulse passes to a 
sensory center, thence directly to a motor center, and so by 
a motor path to the muscle or gland. [Fig. 24; cf. Fig. 3 A.] 




3ZI nerve 

Fig. 24. — Simple Reflex 

Diagram of simple auditory reflex. The auditory stimulus starts an impulse 
through the VIII cranial nerve; ia this reflex the impulse is conducted by an 
intercalary neuron to the origin of the VI nerve, and along this nerve to the 
external rectus muscle of the eyeball, producing a movement of the eye to- 
ward the side. [From Herrick.) 



In higher reflexes the impulse passes from the first sensory 
center to another (higher) sensory center before passing over 
to the motor tract. Sensory and motor centers which lie 
nearest to the receptor or effector organs are called primary 
centers, those next further from the periphery are called 
secondary centers, etc. The lower reflexes pass only through 
the primary centers. In the case of spinal reflexes these 
primary centers lie in the spinal cord near the place where the 
nerves enter. In the cerebral reflexes the primary centers lie 
at the base of the brain. The knee-jerk is a typical example 



SIMPLE REFLEXES 



91 



SKin 



of spinal reflex; ^ winking is a typical cerebral reflex. Sneez- 
ing is another typical reflex, and so is coughing where it occurs 
' involuntarily.' The elaborated cough, like the artificial 
wink, is not a pure reflex. Usually the response in a simple 
reflex is a movement on the same side of the body as the 
stimulus. 

Besides the simple reflexes belonging to the lower levels, 
there are relatively simple responses which involve higher or 
secondary centers. A sudden loud noise often produces vio- 
lent beating of the heart. The sensory impulse in this case 
goes to a higher center, and 
thence passes out through a 
motor pathway connected 
with the cardiac muscles. 

Compound Reflexes. — 
Compound reflexes are those 
in which two or more sen- 
sory impulses are combined, 
or in which a single sensory 
impulse finds multiple ex- 
pression. [Fig. 25.] They 
nearly always involve higher 
centers, though in some 
cases part of the reflex uses 
only a simple arc. Thus the 
knee-jerk may form part of 
a compound reflex; a por- 
tion of the impulse may pass 
over directly from the primary sensory center to the motor 
path and cause the leg to fly up, while part may travel to 
a higher center and lead to some other type of activity. 

If the entire impulse reaches a higher center it may result 
in a coordinated compound reflex. Grasping, sucking, and 

^ It should be said, however, that many physiologists do not regard the 
knee-jerk as a true reflex. 




Fig. 25. — Distributed Reflex 

Stimulation of a receptor in the skin leads to 
contraction of several different muscles Ml, 
M2, M3. [From Herrick.] 



98 REFLEX BEHAVIOR 

certain vocal reflexes are examples of this. In the grasping 
reflex of the hand all the fingers are flexed at once; the sucking 
reflex involves coordinated stimulation of several muscles in 
the lips and tongue. Where higher centers are involved the 
response may be on the opposite side of the body from the 
stimulus; frequently it is bilateral. This is due to the fact 
that the nerves cross to the opposite side of the cord or brain, 
and that the pathways to and from the two sides of the body 
are connected at the secondary centers. 

In reflex action there is usually a certain compounding of 
impulses from the sensory segment of the arc. The eye-wink 
is generally a response to stimulation of the whole field of 
vision, or at least a large area; the reflex of withdrawing the 
hand is usually in response to an impact or temperature 
stimulus which affects many receptors covering a noticeably 
large area. The compounding of sensory impulses is not so 
significant as the motor complication; it serves to intensify 
the effect rather than to complicate the forms of manifes- 
tation. 

In the compounding of reflexes the effect differs according 
to the nature of the component motor impulses. Thus we 
may distinguish between antagonistic reflexes, in which the 
impulses lead to opposing or antagonistic muscles, and al- 
lied reflexes, where the separate impulses tend to reinforce 
one another. In certain cases the impulses tend partly to 
neutralize, partly to reinforce one another; these are called 
allied and antagonistic. Where several reflexes follow in suc- 
cession, they may be alternating (e.g., in walking), or supple- 
mentary (e.g., the flexing of fingers at each joint in grasping). 
Where a completed reflex causes a new stimulation leading to 
another reflex, the series is called a chain reflex. [Fig. 26.] This 
is the border-line between reflex and instinctive activity. 

One further complication of the reflex deserves notice. 
When two separate stimuli, one of which produces a marked 
reflex while the second does not, have frequently occurred in 



COMPOUND REFLEXES 99 

conjunction, it may come to pass in the course of time that 
the impulse due to the second stimulus will discharge into the 
motor path of the first and produce the response which origi- 
nally belonged to the first. If a bell be struck every time that 
the knee-jerk is stimulated, after a while the sound of the bell 
will call forth the knee-reflex response even when the knee is 

Fig. 26. — Chain Reflex 

Stimulation of receptor R produces contraction of effector E, which stimulates receptor R', 
producing contraction of E', etc. C, C = centers. [From Herrick.] 

not touched. This modified activity is called a conditioned 
reflex. It is of considerable importance in intelligent behavior. 

Nature of the Reflex. — The distinctive characteristic of 
the ' pure ' reflex is that the neural paths which constitute 
its arc are definite and the resulting response very precise — 
the motor outgo is not diffuse. Hence, the form of response 
depends almost wholly upon the nature of the present stimu- 
lus, and not upon the retention effect of preceding impulses 
which have affected the same arc. This characteristic is 
modified in conditioned reflexes. 

The relation between stimulus and response in reflex action 
may be stated as follows: (1) The response usually varies with 
the intensity of the stimulus. A very intense stimulation 
generally causes violent contraction. It may also cause a 
more wide-spread effect. Thus the shudder reflex extends 
over a larger part of the body when the stimulus which excites 
it is more intense. 

(2) The nature of the response depends somewhat upon the 
mode of stimulation. The stimulus known as tickling is less 
intense than ordinary touch stimulation, but owing to its 
peculiar quality it causes a much more violent response than 
simple contact. We are familiar with the peculiar effect of 



100 REFLEX BEHAVIOR 

red on the behavior of bulls and other animals; here the * red ' 
quality (mode) of visual stimulation determines the specific 
form of response. 

(3) The response varies considerably with the metabolic con- 
dition of the organism. When certain motor end-synapses 
have been fatigued through frequent stimulations of the same 
sort, the response tends to become less and less intense. This 
fatigue effect is only temporary; after a period of rest the in- 
tensity of response is restored. 

(4) In pure reflexes the retention effect is negligible, but it 
plays an important role in conditioned reflexes. 

Reflex action is the fundamental type of behavior. The 
higher types arise out of it through various complications. 
Instinct and intelligence may both be regarded as consisting 
of the operation of chains of reflex arcs. The chief difference 
between these two types lies in the fact that the neural con- 
nections which determine the pathways and mark out the 
arcs are inherited in the case of instinctive behavior, while in 
intelligent behavior the connections are formed and perfected 
(or modified ) through the creature's individual experience. 

Human Reflexes. — In the human adult comparatively few 
activities belong to the pure reflex type. For the most part 
our motor impulses are modified by complex central im- 
pulses which involve a number of higher arcs. Even such a 
simple reflex as winking may be reinforced or partly inhibited 
by central control; and the same motor paths which carry 
impulses for the winking reflex also conduct impulses for 
' voluntary ' winking and for closing the eye. 

Table III gives the most prominent and important human 
reflexes.. In some cases several allied reflexes are grouped 
under a single head. The autonomic processes (circulation, 
breathing, etc.) may be regarded as a continuous succession 
of reflexes. Since these activities possess no psychological 
interest they are not included in the table. 



Table III. — Human Reflexes 

A. Purest — least subject to central modification in adult 
'Pupillary' or iris reflex Snoring 

Ear twitching (controlled in some Shuddering 

individuals) Starting (to sudden noise, etc.) 

Hand withdrawal (to heat and pain) Trembling 

Myenteric reflexes (operation of Shivering 

stomach and intestinal Rhythmic contractions (in epilepsy, 

muscles in digestion) paralysis agitans, etc.) 

B. Largely pure — subject to inhibition or reinforcement 



Winking 

Accommodation, ciliary reflex 

Eye-fixation and convergence 

Hiccoughing 

Sneezing 

Patellar reflex (knee-jerk) 

Dizziness reflexes 

Yawning 

Vomiting 

Facial reflexes (to bitter taste, etc.) 

Salivation 

Tickle reflexes 



Hand twitching (to dermal pain) 
Plantar reflex (to stimulus on sole of 

foot) 
Great toe reflex 

Vasomotor changes (blushing, paling) 
Breathing changes (to specific stimuli 

and to onset of sleep) 
Sudorific reflexes 
Groaning 
Laughing 
Cramp movements 
Squirming 



C. Occasionally pure, more often centraUy modified 
Coughing Smiling 
Swallowing and gulping Wincing, etc. 
Visceral discharge, etc. Scowling 
Functioning of sex organs Stretching 

Reflexes to odors Convulsive contractions (to deep pres- 

Gasping sure and heat, to pricking and other 

Weeping dermal pains, and to visceral pain) 
Sobbing 

D. Pure in infancy, centrally modified in adult 



Sucking 

Biting and grinding 

Spitting 

Hunger and thirst reflexes 

Lip and tongue reflexes 

Vocal reflexes 

Turning the head 

Tossing 

Grasping (finger reflexes) 

E. Posture reflexes 
Holding head erect 
Sitting 



Tugging (wrist reflexes) 
Clasping (elbow reflexes) 
Reaching (shoulder reflexes) 
Kicking (knee reflexes) 
Stepping (gluteal reflexes) 
Jumping (ankle reflexes) 
Sitting up 
Bending forward 
Rising 



Standing 
Equilibration 



102 INSTINCTIVE BEHAVIOR 

2. Instinctive Behavior 

Relation of Instinct to the Reflex. — The term instinct has 
been variously defined. Earher writers treated it as a mys- 
terious innate power possessed by subhuman animals, which 
enabled them to do the right thing in the right way, without 
consciousness or deliberation. To-day we know that instinc- 
tive activity is the result of integration and coordination of 
nerve impulses, and that the adjustment is due to inherited 
connections between sensory and motor neurons. Even 
among reflexes we find a certain degree of complexity. There 
is no sharp dividing line between compound reflexes and the 
simpler instincts. 

The term instinct will be used here (following many recent 
writers) to denote those complications of behavior which in- 
volve a series of reflex activities, where (a) one reflex fur- 
nishes the stimulus that leads to the next, and (6) the con- 
nections depend upon inherited structure, not upon individual 
modifications. In walking, for example, each step serves 
as a stimulus for the next. When the left foot touches the 
ground the tactile stimulus, acting in conjunction with the 
muscular stimulus in the muscles of the left leg, starts the 
motor impulse for lifting the right leg, and so on. 

In most instincts each reflex in the series involves a different 
kind of reflex from the preceding. A typical example is the 
suckling instinct in the human infant. This involves several 
different reflexes. The first is the bending movement of the 
child toward the breast, a reflex which may be stimulated by 
hunger or by sight or odor. Next is the grasping reflex with 
the lips; then follows the sucking reflex and finally the swal- 
lowing reflex. Each reflex action in this series furnishes a 
stimulus which leads to the succeeding reflex. The grasping 
movement of the lips is stimulated by the touch of the lips; 
the sucking movement by the grasping sensation, and swal- 
lowing by the action of the milk upon the tongue, lining of 



RELATION TO THE REFLEX 103 

the mouth, and glottis. This succession of response and 
stimulation is characteristic of instinctive behavior gen- 
erally. 

A reflex arc is made up of a certain series of neurons or 
neuron groups joined into a circuit. Reflex action takes place 
because the pathway so formed constitutes the line of least re- 
sistance for the discharge of nerve energy. In the same way 
an instinctive circuit-system is made up of several superim- 
posed reflex arcs. Instinctive action takes place because 
each reflex which composes it is a path of least resistance, and 
because the motor response of one reflex provides the appro- 
priate stimulus for the next. 

If when the infant bends forward to seek the breast the lip 
contact is prevented, the lip-grasping reflex is inhibited and for 
the time being the instinct is not completed. The develop- 
ment of an instinct may be thwarted if at any stage the move- 
ment does not lead to the proper stimulus for the next stage. 
As a general rule, however, the same fundamental instincts 
appear in every individual at about the same period of life. 
This is because we all inherit the same fundamental nerve 
structure and live in substantially the same environment. 

Evolution of Instinct. — Each species of animal, mankind 
among the rest, has evolved certain typical kinds of instinc- 
tive behavior. Some types of instinct belong to a wide group 
of species; others to a single species. The origin of wide- 
spread instincts as well as specific varieties may be explained 
on the basis of natural selection, as follows: Each separate 
reflex appeared in the first place in connection with some 
chance variation of nerve structure; the variation was se- 
lected and has survived because it is suited to the needs of 
the creature. The grouping of reflexes into instincts is also 
the result of structural variations due to chance, which have 
survived on account of their utility. If a new combination of 
reflex paths, brought about by a chance variation in growth, 
prove especially fitted to preserve the animal's life, it has a 



104 INSTINCTIVE BEHAVIOR 

greater chance of surviving and being transmitted to pos- 
terity. 

The combination of reflexes into coordinated instincts is due 
to the growth of the fibers of their constituent neurons in cer- 
tain directions. If the motor neurons of one arc grow in such 
a way that their effectors cooperate with the receptors and 
sensory neurons of another arc, the two may act together and 
bring about instinctive activity. But not all such combina- 
tions are advantageous. In the suckling instinct of the human 
infant, for example, the combination of activities whereby 
the act of grasping with the lips stimulates directly a sucking 
reflex, is a distinct advantage to the child. If a variation 
should occur whereby the lip-grasping reflex results in stimu- 
lating some entirely different movement, the combination 
might be distinctly disadvantageous and lead to the child's 
untimely death. Some of our fundamental instincts, such as 
rage and fear, were presumably of advantage originally to their 
possessors. The resulting movements of aggression or de- 
fense served to ward off threatening danger. These instincts 
are no longer advantageous to civilized man; but instead of 
being weeded out by natural selection they are suppressed 
individually by intelligent inhibition. 

Classes of Human Instincts. — The human adult seldom 
behaves in a purely instinctive manner. His activities are 
largely modified and controlled by individual experiences; 
they belong for the most part to the intelligent type. Even 
the basal instincts are partly suppressed and reduced to 
conventional forms. There are two modes of behavior in man 
which take the place of pure instincts: modified instincts and 
instinctive tendencies. 

Modified instincts include the partly inhibited expressions 
of anger, fear, and the like; also partly trained activities, such 
as walking, feeding, parental and sexual instincts, expression of 
sorrow and delight. In all such cases the instinctive mechan- 
ism is a fundamental feature; but individual experience, es- 



CLASSES OF HUMAN INSTINCTS 105 

pecially the social example of our fellow men, leads to radical 
changes in the form of behavior. 

There have been wide differences of opinion among psy- 
chologists as to the number of human instincts. James and 
others insist that man possesses a great variety of instincts 
— as many, in fact, as any of the lower species. Other writers 
restrict human instincts to a few kinds. Both views are 
partly correct. Few pure instincts are found in the human 
adult, but a great number of modified instincts. It would not 
be proper to treat these as forms of intelligent behavior, yet 
strictly speaking they are not true instincts. 

It is difficult to classify human instincts on the basis of their 
origin, because some arise from a combination of several dif- 
ferent factors. To a certain extent we may divide them ac- 
cording to the specific vital function ^ which they promote. 
But this does not carry us far, for growth, repair, and regu- 
lation are not promoted by any specific instincts, except 
(indirectly) by those which are also concerned in nutrition. 
The (a) nutritive and (6) reproductive functions each form the 
basis of certain deep-rooted instincts. The active relations 
between man and his environment give rise to two further 
varieties which are termed (c) defensive and {d) aggressive 
instincts. Biological organization as such is not associated 
with instinctive behavior, but the organization of individuals 
into groups is promoted by certain (e) social instincts. 

Table IV gives the chief kinds of instincts in each of these 
five groups. The filial instincts of infants do not properly be- 
long among adult instincts, but are inserted because of their 
close relation to the maternal instincts. Primitive forms of 
certain types are given in brackets. 

Metabolic expression includes a variety of complex manifes- 
tations of general bodily or ' systemic' conditions (joy, sorrow, 
etc.) Some of the defensive and aggressive instincts are usu- 
ally social in their manifestations. The instincts of subjection 

^ See ch. ii. 



106 INSTINCTIVE BEHAVIOR 



Table IV. — Human Instincts 

1. Nutritive 2. Reproductive 

Metabolic expressions Mating (sexual attraction^ 

Walking courtship) 

Feeding Maternal 

Wandering [Hunting] Filial (of infancy) 

Acquiring [Hoarding] 

Cleanliness 

3. Defensive 4. Aggressive 

Flight Fighting 

Subjection Resenting 

Hiding Domineering 

Avoiding Rivalry 

Modesty [Shyness] 
Clothing [Covering] 
Constructing [Home-making] 

5. Social Organization 
Family (parental and 

filial) 
Tribal [Gregarious] 
'Apopathetic' 
Sympathetic 
Antipathetic 
Cooperative 



and rivalry generally involve social relations between man 
and man; the domineering instinct may have as object either 
human beings or lower animals. 

The family instincts have apparently a different origin 
from the gregarious and other types which follow in the list. 
Parental and filial instincts are based essentially upon sex 
relations, while the tribal instincts are due to stimuli which 
are only remotely traceable to the reproductive life. In 
some human races the general social stimuli are weak, and 
tribal association is lacking; but family life may exist without 
community life. 

The instincts termed ' apopathetic ' (for want of a better 
name) are responses to the attitudes of others. Thorndike 



CLASSES OF HUMAN INSTINCTS 107 

notices a variety of types: (1) We act in certain ways when 
others are present, even though they are not concerned with 
our doings. (2) We respond differently when they enter into 
communication and relation with us. (3) We respond in 
specific ways to the approval of others, and (4) to their scorn. 

Instinctive Tendencies. — An instinctive tendency is a mode 
of behavior comprising many distinct sorts of action, all of 
which are individually learned, but which resemble one an- 
other in general type; the ' type ' itself is not learned but be- 
longs to the constitution of the species. 

Table V gives a list of instinctive tendencies belonging to 
the human species. The most fundamental types are imita- 
tiveness, 'playfulness, and curiosity. 

Table V. — Instinctive Tendencies of Man 

>' Imitativeness 
li Playfulness 
•^ Curiosity 

Dextrality (right-handedness) 

Esthetic expression 

Communicativeness 

The relation between inherited and acquired factors in in- 
stinctive tendencies is best illustrated in the case of imitation. 
Every imitative act is individually acquired; but there are 
distinct inherited paths of nervous connection which facili- 
tate certain kinds of response that reproduce (' imitate ') the 
movements of other beings. To illustrate from other species, 
the parrot is able to imitate many modes of vocal expression, 
and the monkey is able in the same way to imitate gestures. 
But the parrot has no mechanism for reproducing gestures, 
nor the monkey for reproducing articulate expression. 

In the human child and adult the underlying instinctive 
tendency to imitate includes not only vocal expression and 
gesture, but muscular movements of almost every sort. The 
specific acts which we perform when we imitate are learned, 
but the direction taken by the learning process is based upon 



108 INSTINCTIVE BEHAVIOR 

an inherited tendency in the nervous make-up of man. In the 
same way curiosity manifests itself in different ways accord- 
ing to the individual — in exploration, study of nature, lis- 
tening to gossip, etc. 

Play is partly an imitative phenomenon. Many children's 
games are due to imitation of the serious activities of adult life. 
Learning any specific game may be an imitative act. But the 
play-instinct has a distinctive character of its own; play means 
a tendency to perform acts which are not directly concerned 
with one's mental and vital welfare. This is characteristic 
of all play, whether imitative or spontaneous, social or soli- 
tary. Such widely different activities as ' playing telephone,' 
a game of foot-ball, a solitary game of cards, a ramble in the 
woods, have one common feature: they represent relaxa- 
tion from the serious business of life. 

Right-handedness, more properly called dextrality,^ is the 
preference of one hand or the other in performing manual 
acts; in a majority of cases the right hand is preferred (dextro- 
dextrality), though in many individuals the left is dominant 
(sinistro-dextrality). The tendency is supposed to rest upon 
a greater development of certain motor centers in one cere- 
bral hemisphere, and is probably connected with the forma- 
tion of the speech center, which is usually found in the left 
side of the brain. (The left hemisphere controls the right side 
of the body and vice versa.) 

Esthetic expression, the ' artistic touch ' which many human 
acts exhibit, has not as yet received any satisfactory explana- 
tion. The tendency to communicate manifests itself in many 
ways, such as gesture, speech, etc. which are developed sys- 
tematically by intelligence. Certain acts classed among the 
instincts may also be regarded as instinctive tendencies. Chief 
among these are acquisitiveness, constructiveness, companion- 
ship (tribal instinct), and mastery (domineering instinct). 

^ Psychol. Bull., 1909, 6, p. 131. The term ambidextral is preferable to 
ambidextrous. 



DEVELOPMENT OF INSTINCTS 109 

Development and Variability of Instincts. — Instincts and 
instinctive tendencies, like reflexes, are inherited. They 
belong to the original inborn constitution of each individual. 
The nerve structure through which they operate is provided 
for in the original germ cell from which the individual grows^ 
and is derived directly from one parent or both. This does 
not mean that a given instinct is present at birth or that the 
appropriate neural connections are already formed at birth. 
In most cases the structural basis for the instinct is ' practi- 
cally ready ' at birth and in some cases long before birth ; but 
the manifestation of the instinct depends upon the first stim- 
ulation, which may occur at some later period of life. 

In certain instincts the welding of the chain of stimuli is 
not completed till a considerable time after birth. Human 
walking, for example, is usually not completely adjusted till 
some time in the second year of postnatal life. The repro- 
ductive functions reach their full development only at sexual 
maturity, usually between the tenth and fifteenth years. 

In short, any given instinct begins to manifest itself at a cer- 
tain period of life, and the period at which it appears depends 
not so much upon the chance occurrence of appropriate stim- 
uli, as upon the perfection of the nerve mechanism. If the 
proper stimuli do not occur at the right season, the appear- 
ance of the instinct is delayed, and in special cases it may 
never be perfected. It should be remembered that the evolu- 
tion of any instinct depends upon the general conditions of life 
in the species which has perfected it, and especially upon the 
presence of a definite type of environment in which all its mem- 
bers live; hence only in rare cases would the appropriate stim- 
ulus for a basal instinct be lacking. 

Even a pure instinct is not invariable. Its form of expres- 
sion depends primarily upon the nature of the initial stimulus 
in the chain, but it is modified by the influence of other stim- 
uli which occur as the act is being performed. The rapidity, 
force, and motor manifestations of the suckling instinct vary 



110 INSTINCTIVE BEHAVIOR 

considerably with the infant's sense of hunger. In the adult, 
the effect of accompanying stimuli is readily noticed in the act 
of walking. We adjust our locomotor movements in different 
ways when we step up or down, walk on a slope, avoid a stone 
in the path, etc. Some of these modifications result from dif- 
ferences of pressure on the sole of the foot, others are due to 
visual stimuli from objects ahead. Nor is this altogether a 
matter of ' consciousness.' We adjust our walking movements 
to slopes and obstacles quite as well when engaged in con- 
versation as when we are paying strict attention to the path 
in front. We step down from the curb or walk around a tree 
often without being aware that we are doing so. 

These motor adaptations are due to variations and different 
combinations of stimuli. The chief difference between the 
variations which occur in instinctive and intelligent behavior 
is that instinctive modes of expression are not altered by past 
experience, while intelligent expression depends essentially 
upon the effects of retention. 

If instinctive expression is not modified by experience, how 
is it that walking and other instincts show the effect of learn- 
ing.'* The explanation is that in such cases certain inherited 
paths or lines of neural conduction are broken up and other 
pathways are substituted. To the extent that this occurs 
the behavior loses its instinctive character. In the complex 
cortex of the human brain the higher centers gather in and 
send out impulses which inhibit certain reflexes and reinforce 
others. The effect of this is to transform the response little 
by little from the instinctive to the intelligent type. The 
modified instincts lie midway between these two types. Our 
adjustments in walking are due to past experiences of stepping 
up or down and avoiding obstacles; but the general coordina- 
tion of locomotor activity is instinctive. 



DEVELOPMENT OF INSTINCTS 111 

Collateral Reading: 

James, W., Psychology, ch. 26. 

Morgan, C. L., Instinct and Experience, chs. 1-4. 

McDougall, W., Social Psychology. 

Thorndike, E. L., Educational Psychology, (briefer course) chs. 3, 5. 

Angell, J. R., Psychology, ch. 15. 

Watson, J. B., Behavior, chs. 2 (II), 4, 5. 

Parmelee, M., Science of Human Behavior, chs. 11-13. 

Meyer, M., Fundamental Laws of Human Behavior, chs. 2-4. 

Hough, T., Classification of Nervous Reactions, Science, 1915, 41, 401-418. 

Blanton, M. G., Behavior of the Human Infant during the First Thirty 
Days of Life, Psychol. Rev., 1917, 24, 456-483. 

Drever, J., Instinct in Man, chs. 7, 8. 

Loeb, J., Mechanistic Concept of Life, ch. 3 (sees. 1-3). 

Loeb, J., Comparative Physiology of the Brain and Comparative Psy- 
chology, ch. 13. 

Driesch, H., Science and Philosophy of the Organism, Vol. II, Part III, 
ch. 2. 

Woodworth, R. S., Dynamic Psychology, ch. 3. 

Practical Exercises: 

Report all noticeable right or left preferences in your actions; e.g., which 

arm or leg acts first in putting on or removing your garments. 
Analyze the processes included in three dififerent human instincts, e.g., 

eating, walking, defensive behavior. 
Examine why you have the following tendencies: (a) to sympathize with 

friends; (6) to collect objects of some kind; (c) to find out things you do 

not know. 



CHAPTER VII 

BEHAVIOR (continued) 
3. Intelligent Behavior 

Nature and Neural Basis of Intelligence. — If similar 
stimuli be applied to the same individual repeatedly, the re- 
sponses which follow may differ from time to time. This 
variability, which characterizes certain kinds of activity, es- 
pecially in the higher vertebrates, does not throw doubt upon 
the uniformity of nature; it means simply that conditions 
within the organism have altered. There are two distinct 
types of individual modifications in behavior, due to fatigue 
and adaptation, respectively. 

(a) The fatigue effect occurs in instinctive actions and re- 
flexes as well as in intelligent actions. Constant repetition of 
the same stimulus produces a katabolic condition of the re- 
ceptors (fatigue) which tends to weaken or inhibit the re§ponse. 
This effect disappears after a period of rest. 

(6) The adaptation effect acts in the opposite way. It is 
not an impairment of the response through weakening of the 
impulse, but a distinct improvement due to more perfect 
adjustment. In neural terms, it is not the effect of katabol- 
ism, but the formation of new nerve paths or increase in the 
efficiency of old paths. Adaptive modification of response 
is characteristic of intelligent behavior, and differentiates it 
from instinct. 

Although the instinctive type of behavior predominates in 
subhuman species, a certain degree of adaptive modification 
through individual experience occurs in all animals except 
possibly those well down in the scale. Experiments with the 
maze [Fig. 27] demonstrate this. An animal is released at 
the entrance (A) of a maze, food having been placed at the 



NATURE OF INTELLIGENCE 



113 



far end or center (B). The hunger stimulus, :reinforced by 
the odor stimulus, arouses his locomotor activity. He starts 
off and after a certain number of hesitations, false moves, and 
retracings reaches the food and satisfies his hunger. The 









Fig. 27. — Mazes for Investigating Habit Formation 

Two mazes used in experiments on rate of learning path from A to B. Upper figure is a 
simple type used by Yerkes with frogs. One choice of paths at start, one choice near end. 
IFrom Harvard Psychol. Studies.] 

Lower figure, maze used by Hubbert with rats. Heavy line shows actual path of one rat on 
6^ trial. See Table VI, p. 123, tor results of this experiment. [From J. of Animal Behavior.} 



114 INTELLIGENT BEHAVIOR 

same program is repeated on the same or successive days. It 
is found that after a number of trials the animal succeeds 
in reaching the food-box in a shorter time, and with fewer 
false moves as indicated by the total distance traversed. In 
an experiment with 27 white rats the average time was reduced 
from 467 seconds in the first trial to 40.3 in the eleventh, and 
the average distance from 4216.1 to 1029.8 cm.^ Even in 
species as low as the crayfish and other Crustacea there is a 
slight reduction in time and distance after many trials in a 
simple maze. 

Adaptive modifications ^ of behavior are not limited to 
improving the efficiency of responses. The most important 
modifications are those which bring about new modes of re- 
sponse. Human behavior is far more subject to this kind 
of modification than the behavior of any subhuman species. 
In the human child we observe any number of instances in 
which new forms of response are developed through indi- 
vidual experience: talking, manipulating knife, fork, and 
spoon, buttoning the clothes, opening the door, climbing 
stairs, folding a napkin, writing, swimming,^ riding a bicycle, 
etc. The three last are occasionally developed in later life. 
Generally adult acquisitions are concerned with more com- 
plex processes, such as steering a sail-boat or motor-car, type- 
writing, telegraphing, shooting, etc. 

The growth of adaptive modification is illustrated in the 
behavior of the child at various ages when confronted by a 
closed door. A very young child will respond by weeping or 
calling out. As he grows older he may push upon the door or 
pound vigorously — two alternative modes of response which 
are both quite different from the earlier. Later the child may 

1 See Table VI, p. 123. 

^ It is usual to distinguish between modifications, or changes individually 
acquired, and variations, changes brought about in the germ cell and in- 
herited in the individual. 

' Learning to walk is due to the growth of inherited paths and belongs 
rather among the modified instincts (ch. vi). 



NATURE OF INTELLIGENCE 115 

shake the handle, and finally he may turn it and push or pull 
on the door. This last form of response persists and the others 
are suppressed. 

Intelligence is the capacity to acquire and perfect new modes 
of response through individual experience. This capacity de- 
pends upon the presence of certain conditions in the neural 
constitution of the organism: 

(1) The central system must contain alternative neural 
pathways. This condition is fulfilled if the central neurons 
are provided with a number of collaterals connecting with 
various higher and lower neurons. 

(2) The connection with these collaterals must be plastic; 
that is, certain synaptic connections must not be so firmly 
established by inheritance that the impulse will always pass 
over one path to the exclusion of other alternatives. 

(3) The resistance at alternative synapses must be capable 
of change independent of one another, so that a pathway 
which at one time is a line of greater resistance to the passage 
of the impulse may later on become the line of least resistance. 

In man an intricate inherited system of multiple connections 
exists in the higher centers and particularly in the cortex of 
the cerebrum. This complex system includes a vast number 
of alternative paths which fulfil the above conditions. The 
complexity of the human cortex is an essential condition of 
man's superior intelligence as compared with other species. 

Intelligence and Habit. — We have noticed the division 
of intelligent behavior into habits, communication, rational ac- 
tions, and conduct (ch. ii). The three last are higher stages of 
development which may be left for discussion till later chap- 
ters. The fundamental type of intelligent activity is habit. 

The term habit, like instinct, has been used in a variety of 
ways. In contemporary psychology it denotes a more or less 
fixed mode of response which has been acquired individually. 
The process of acquiring a habit is called habit-formation or 
learning. 



116 INTELLIGENT BEHAVIOR 

Some writers draw a distinction between intelligence and 
habit, on the ground that intelligent behavior is subject to 
constant modification, while habits are fixed. In reality, the 
antithesis is only partial. Even where no firmly established 
habit exists, there are cases where the most ' intelligent ' or 
suitable response will be repeated time and time again; and 
on the other hand deeply fixed habits are usually essential fac- 
tors in the most plastic, intelligent modes of behavior. 

For instance, certain persons are ambidextral; but even with 
such individuals it is more suitable to use the right for hand- 
shaking, since the other person customarily extends his right 
hand, and the clasping of two right hands is easier than right 
with left. Hand-shaking behavior therefore tends to take a 
definite form even before it becomes fixed as a neural habit. 

The organization of intelligent behavior is a continual proc- 
ess of habit-formation. Letter-writing is a typical intelligent 
activity; yet an essential factor in its successful accomplish- 
ment is a deeply fixed habit of manipulating the pen and of 
forming each letter or word in a definite manner. Every in- 
telligent response consists in large part of habitual move- 
ments or well established motor attitudes. 

The Learning Process. — The term learning is used to de- 
note the process of forming new connections in the nervous 
arc and perfecting such connections through repetition. It 
includes both the process of motor habit-formation and the 
acquisition of ' central ' habits. When we memorize the 
multiplication table or learn to think logically, the acquisition 
is central rather than motor. ^ 

Learning, or habit-formation, includes two opposite factors : 
(a) a tendency to alter the response (or the central process), 
and (6) a tendency to respond (or to think) repeatedly in the 
same way. The learning process which is typical of intelli- 

^ The central material of mental life will be examined in later chapters-, 
since the learning process is the same for thoughts as for motor acts it is 
convenient to discuss both phases together. 



THE LEARNING PROCESS 117 

gence may therefore be explained as the result of cooperation 
between two distinct and opposite processes, called Acquisi- 
tion and Fixation. 

a. Acquisition. — Acquisition is the process of establishing 
new paths of neural conduction in the central part of the 
nervous arc. Instinctive acquisition is a racial product and 
depends upon the structural evolution of the nervous system. 
Intelligent (or individual) acquisition is not due to the develop- 
ment of neural structure. It does not involve the forma- 
tion of new neurons nor the projection of new collaterals. 
The neurons concerned are already in existence and all the 
branches which interconnect them have been formed in pre- 
natal life. Neither does it involve extension of the dendrites, 
axons, or collaterals of existing neurons.^ The interconnect- 
ing lines of conduction and synapses are usually present long 
before the actual physiological connections are made. 

Intelligent acquisition depends rather upon changes of rel- 
ative resistance at alternative synapses.' There is either 
increased tension at certain synapses, so that the impulse is 
diverted from the path which was previously the line of least 
resistance; or else the tension at alternative synapses is de- 
creased so that the nerve impulse passes across at these points 
more readily than heretofore. In either case the path of neu- 
ral conduction is altered, provided the change of tension is so 
great that the relative resistance of the two lines is reversed. 

Just what causes this altered resistance has not yet been 
fully determined. 

(1) Change in relative resistance may be brought about by 
metabolic variations in the synapses themselves, due to dif- 
ferent nutritive conditions at the several points. If the syn- 
apse between A and Bl [Fig. 28] undergoes katabolism while 
that between A and B2 undergoes anabolism, the path of the 
impulse may be shunted from A — Bl to A — B2. 

(2) A condition of lessened tension in the neuron connect- 

1 See Fig. 4. p. 34. 



118 



INTELLIGENT BEHAVIOR 



ing at one of the alternative synapses may increase the per- 
meability of that synapse. This may occur if an impulse from 
another path pass through this higher neuron simultaneously 
with the given impulse or just before it. If an impulse pass 




Fig. 28. — Changes of Path in Habit Formation 

Diagram to illustrate the shunting of impulses from path A — Bl to path 
A— B2, etc. (See text.) 

through the neuron B3 at the same time as the impulse in A, 
the tension between A and B3 may be so lessened that the 
impulse in A will take the path A — B3 instead of A — Bl. 

(3) A third cause of change may be the intensity of the 
present stimulus. The impulse may be so intense that it will 
not only pass over the usual synaptic path from A to Bl, 
but will also drain out through other synapses into B2, B3, 
etc., at the same time; just as a heavy stream of water may fill 
the usual channel and find its way along other lines besides. 

(4) Finally, the resistance of a synapse may depend upon 
the mode of the retention trace in the further neurons. If the 
mode of the nerve impulse has the significance which we have 
suggested (ch. iv), then the impulse will pass more readily into 



ACQUISITION 119 

a neuron which has formerly been affected by the same hind 
of impulse and which has retained a set corresponding to this 
mode. Thus if the present impulse in A be similar in mode 
to the trace in B4, it may take the path A — B4 instead of 
the path A — Bl, 

It seems probable that alterations in nerve paths are due to 
each of these factors : (1) varying metabolic condition of the 
synapses; (2) varying tension in the higher neurons; (3) in- 
tensity of present impulse; and (4) modal relation of present 
impulse to the retention trace in the higher neurons. 

Of one thing we may be reasonably assured. The change 
in the neural connections is not due to a mysterious guid- 
ing agency outside of the nervous mechanism. There is no 
ground for assuming the existence of a sort of telephone oper- 
ator within us, whose duty it is to plug in certain connections 
and remove others. The shunting process which leads to new 
acquisitions depends upon neural conditions, and upon the 
nature of the impulse itself.^ 

We may group the operations concerned in acquisition 
under three heads: (1) Accommodation, or formation of new 
paths. (2) Inhibition, the blocking of old pathways. (3) Cen- 
tral reinforcement, cooperation of simultaneous impulses in 
the higher centers. The laws of acquisition may be stated 
in terms of these three processes. 

(1) Law of Accommodation: New pathways may be 
opened by the occurrence of anabolism at some synapse or 
in some connected higher neuron, or by the extreme inten- 
sity of the present impulse, or by modal similarity between 
the present impulse and the retention trace in some con- 
nected neuron. This brings about a new form of response. 

(2) Law of Inhibition: A pathway hitherto used may be 
blocked by katabolic conditions in some synapse or further- 
lying neuron, or by modal dissimilarity between the present 

^ See Appendix, "Conscious Purpose," p. 427; "Personification of Natural 
Phenomena," p. 433. 



120 INTELLIGENT BEHAVIOR 

impulse and the retention trace in some neuron in the circuit. 
This checks the customary form of response. 

(3) Law of Central Reinforcement: A central process 
which occurs simultaneously with a given impulse or imme- 
diately precedes it, may open a new path of discharge for the 
latter and thus produce a new response or a more complex 
mode of response. 

The operation of these laws may be readily noted in many 
of our adaptations to new situations. In reading aloud, when 
we see a new word the nerve impulses are shunted into va- 
rious neurons whose retention traces correspond in mode to 
the several letters or syllables in this word; the result is an 
accommodation of response. When we see a familiar figure 
approaching we prepare to greet the individual in one of the 
usual ways; if on closer inspection it prove to be a stranger, 
the mode of impulse becomes altered, and the bow or saluta- 
tion is inhibited. When we are walking to the station and 
hear the whistle of our train the auditory impulse combines 
with the impulses concerned in the act of walking, and this 
central reinforcement brings about a new — in this case a 
livelier — motor response. 

A case of inhibition combined with accommodation is ob- 
served when we start to wind a clock. If we find that the 
key does not readily turn in one direction we thereupon al- 
ter the course of the motor impulse, which results in our turn- 
ing the key in the opposite direction.^ 

b. Fixation. — Fixation is the second general operation in- 
volved in habit-formation. It depends upon the repetition of 
impulses of the same sort. If the same mode of impulse recur 
over and over again, this repetition tends to improve the 
synaptic connections in the central neurons through which 
the impulse passes, and thereby increases the tendency to 
motor discharge along the same pathway. The result is 

^ Charles Lamb gives an amusing instance (not to be taken literally) of 
non-acquisition in his essay on Roast Pig. 



FIXATION 121 

brought about more quickly by very Intense stimulation; 
that is, in case of powerful excitation the improvement ad- 
vances more rapidly and fewer repetitions are needed. Since 
the condition of the synaptic connections is subject to altera- 
tion from time to time, fixation advances more rapidly also if 
similar impulses recur before too long an interval elapses. 

Thus after a new path has been acquired, the new mode 
of response to which it leads tends to become fixed by 
(1) repetition of similar impulses, and the process is aided 
by (2) the intensity of the impulse, and by (3) the recency 
of the acquisition.^ 

The rate of progress in fixation is greater if no conflicting 
mode of response occurs meanwhile which would open up dif- 
ferent paths of discharge. Fixation is impeded when after 
starting to learn on one typewriter we change to another ma- 
chine with a different keyboard; here we are brought face to 
face with conflicting modes of response, which retard the 
fixation of definite paths. 

The measurement of the progress of fixation in units of 
increased speed and decreased errors is an empirical problem 
which has been investigated for many common habits. Ex- 
periments on the rate of learning have been made in the case 
of typewriting and other definite habits, such as telegraphy, 
juggling balls, shorthand, mirror- writing,^ etc. 

An interesting practical problem in this connection is 
whether progress in fixation is more rapid where the repeti- 
tions are crowded into a short period of time, or where they 
are spread out over a longer period interspersed with intervals 
of rest. Contrary to the general impression, it has been 
found that progress in memorizing is faster in the long run 
with shorter practice periods interrupted by rather long rest 

^ See ch. xvi, "Laws of Ideational Suggestion," pp. 338-342. 

2 Mirror-writing by looking into a mirror and making letters which 
look correct in the mirror) involves the breaking up of deeply fixed habits. 
The experiment is easily arranged and gives interesting results. 



n^ INTELLIGENT BEHAVIOR 

intervals. But the progress in memorizing a set speech is 
faster if it be learned as a whole than if it is split up into parts 
and each part is learned separately. 

Fixation is characterized by two distinct changes in the 
neural operations. (1) Increased ease of connection among 
the neurons, whereby the time of reaction is shortened. This 
effect is called facilitation. (2) Weakening of diffused im- 
pulses at the coordinating centers, so that certain accom- 
panying movements which play no definite role in the act 
gradually drop out. This is called elimination. The laws of 
fixation may be stated as follows: 

(1) Law or Facilitation: Repetition of the motor dis- 
charge along a newly acquired path improves the connections 
of the neurons through these synapses, and thereby renders 
the new mode of response quicker and easier. 

(2) Law of Elimination: As the new connections improve, 
the motor discharge tends to pass over the given path with 
less diffusion over other paths; this results in cutting out 
useless movements and increases the precision of the response. 

These laws may be verified by examining the fixation of 
some common habit, such as typewriting. After continued 
practice we find it easier to strike the right key, and the opera- 
tion proceeds more quickly. At the same time useless move- 
ments are avoided; the finger descends directly on the proper 
key, instead of hovering over the keyboard. There are fewer 
eye movements of search. The subject no longer wrinkles his 
brow, puckers his lips, and breathes hard. One can readily 
note in himself any number of useless movements, due to dif- 
fuse discharge, when he undertakes the formation of a new 
habit. 

The balancing movements of a child when he begins to 
walk furnish another illustration. The disappearance of these 
useless movements means that the entire nervous energy is 
directed along the appropriate path; in terms of response it 
means greater precision. An instance of complete fixation is 



FIXATION 123 

the case of learning to locate an electric-light switch quickly 
in the dark. 

Table VI. — Progress of Learning 

A. Habit Formation in the Rat: 

Trial Av. Time (sec.) Av. Dist. (cm.) 

1 467.0 4216.1 

6 186.6 1719.2 

11 40.3 1029.8 

16 25.5 868.4 

21 24.2 739.9 

26 26.1 756.5 

31 31.8 593.2 
Average attainment of 27 white rats in maze experiment. Two trials each 

day; animal allowed to feed after second trial. (H. B. Hubbert, /. of 
Animal Behavior, 1914, 4, p. 63.) 

B. Habit Formation in Man: 

Day Av. Time (sec.) Av. No. of Errors 

1 79 29 

2 72 27 

3 63 14 

4 60 10 
6 56 7 

6 54 4 

7 53 2.5 

8 49 2 

9 47 0.25 

Average attainment of 4 human subjects learning to typewrite nonsense 
groupings of 7 different letters, arranged in a series of 55 letters. The series 
was performed 3 times daily. Table shows average time and average number 
of errors per series. (J. H. Bair, Psychol. Monograph, No. 19, p. 17.) 

Table VI gives the results of two experiments on motor 
learning — one with white rats, the other with human adults. 
In each case the increase in facilitation is shown by the 
diminution of time (column 2) ; elimination of useless move- 
ments is indicated in the first case by decrease in distance 
traversed, in the second by decrease in the number of errors 
(column 3) . Fig. 29 shows the progress of facilitation in learn- 
ing to telegraph. The curve represents the number of words 
* tapped off ' in five minutes on successive days. 



124 



INTELLIGENT BEHAVIOR 



Adaptation to New Situations. — It is seldom that we find 
ourselves twice in exactly the same situation. While the gen- 
eral situation may resemble some past experience, there are 





















--' 


100 


1 








^i 




-. 4 


90 _ _ _ 


J X 




-Sv 




Y> 4 




t\t 


80- 1^- 


1^ -Xt 


^ z 


e it-. ^ 




^-•'XJ 


_i 


^i 


70- i 




- ^ I 




7 




t 




6o_ ^ _. 




K ^ 




j7 




t 




so — -t^ —i 




0'^ ~ / 




~^^ 




1 




An- - t 




40 f 




^^ 




jt 




r»o- ix i 




30 - t i 




t J 












20 - ^ -^ - - 




. 












10 ~ ~ 

















10 



15 



20 



25 



30 



35 



40 



Fig. 29. — Curve of Learning 



Vertical numbers denote number of words which observer was able to telegraph in 5 minutes 
after 30 minutes of practice. Horizontal numbers denote successive days of trials. Total un- 
familiarity with habit at start. [From Swift, in Psychol. Bulletin.] 



ADAPTATION TO NEW SITUATIONS 125 

usually signijficant differences between our surroundings in 
the two cases. When we set about to dress, our clothes are 
not always in the same place. We have different errands to 
perform daily on our way to business. We study different 
subjects and write different lectures on successive days. 

The fixation of certain modes of activity enables us to per- 
form the stereotyped portions of our responses to the present 
situation. But how comes it that our responses to the new 
factors in the situation are usually fit or suitable? The modi- 
fications of response described under acquisition may or may 
not result in making the outcome more suitable. Yet in a ma- 
jority of cases the modified response is fairly well adapted to 
the situation if the latter is not altogether novel. This adap- 
tation requires explanation. 

There are two ways in which adaptation is attained: 
(1) through trial and error, and (2) by mnemonic combination. 

(1) Trial and Error adaptation depends upon inhibition 
and the persistence of the nerve impulse. If the response to 
a novel situation is not suitable, it frequently results in check- 
ing the motor impulse and starting a discharge along some 
other pathway. Inhibition may occur again if the second 
response is unfit, and so on till an adapted response is ' hit 
upon.' This type of adaptation occurs in solving a problem 
or puzzle, in inventing apparatus, in finding one's way, etc. 
It does not produce immediate success, and does not ac- 
count for the high degree of adaptation exhibited in human 
behavior. 

(2) Mnemonic Combination, or associative memory, de- 
pends upon the fact that in most situations, although the 
grouping of stimuli is novel, the elementary components 
are individually similar to previous stimuli. These elemen- 
tary stimuli in the past have left retention traces in the central 
nervous system. When the same stimuli recur in a new group- 
ing the pathways bearing these traces will (it is assumed) be 
brought into connection, and will be combined in new ways. 



126 INTELLIGENT BEHAVIOR 

This will modify the form of response. Since the separate 
retention traces were due to conditions which resemble the 
present, the new response will tend to be adaptive. It is 
owing to such mnemonic combinations that our dressing pro- 
ceeds smoothly even when our clothes are hung in a different 
closet or stowed away in another drawer, that we perform dif- 
ferent errands on successive days, consult different text-books, 
and so on. 

Behavior based upon mnemonic combinations is adaptive 
insofar as the elementary responses which it involves are 
adaptive. In adult life the simpler habits have already been 
formed. Hence our behavior in complex situations involving 
combinations of simple habits tends to be adaptive also. But 
it is not always so. We sometimes go to the desk or bureau to 
get something and stand helpless, having forgotten what we 
were after. Or we search everywhere for our pencil only to 
find it at last behind our ear. Occasionally in complex actions 
the mnemonic combinations are crossed. We light our cigar 
with a match, toss the cigar away, and start to put the match 
into our mouth. These failures in adaptation are rare, how- 
ever, compared with the successes.^ 

Growth of Intelligence. — Intelligence, like instinct, is a 
phylogenetic growth. It evolves gradually from lower to 
higher species of animals as the nervous system increases 
in plasticity. The maze experiments described above furnish 
a measure of quantitative progress as we ascend the animal 
scale. The qualitative progress of intelligence is determined 
by testing the ability of various species to open gates or prob- 
lem-boxes with complicated fastenings, and to solve other com- 
plex problems. The chief interest of such tests in relation to 
human psychology is the wide gap which they reveal between 
the highest subhuman modes of intelligent behavior and 
those exhibited by the human adult. The intermediate steps 

^ The central processes involved in adaptation will be discussed later. 
(See especially chs. xi, xiii, xix.) 



GHOWTM of intelligence i27 

are supplied by the successive stages of mental development in 
the human child. ^ » 

Biological or vital growth is characterized by changes and 
differentiations of structure. Mental growth is ' functional ' 
development; it is characterized by greater coordination of 
response or greater complexity of the central integrations. 
Moreover, it is determined by present capacity rather than 
by past accomplishments. The stage of intelligence which 
a given individual has reached is measured not by what he 
has actually accomplished but by what he is able to do. When 
we say that man ' can draw,' we do not mean that he has made 
every possible movement used in drawing, but that his move- 
ments are so coordinated that he is capable of combining 
drawing movements of various sorts with great precision. 
When we say that a man can speak English we do not mean 
that he has uttered every word in the dictionary, but that he 
is capable of uttering a large number upon their being sug- 
gested. 

This applies to integration as well as to coordination. A 
man is said to know how to extract square roots even though 
he has never extracted every square root under a million. 
The measure of his stage of development is his ability to per- 
form the process in any sample case. In other words, growth 
in behavior (and growth in organization of conscious experi- 
ence as well) means a certain capacity, not necessarily an actual 
attainment. This distinction applies alike to reflexes, instincts, 
and intelligence. 

In the human species intelligent behavior develops gradu- 
ally and may continue to progress until far beyond middle life. 
Each intelligent act depends upon the perfection of certain 
component acts and when perfected may lead in turn to more 
complex developments. 

The act of writing depends upon our ability to move the 

^ It is well worth while to observe closely the acquisition and fixation of 
relatively simple habits in the child at various ages. 



1^8 INTELLIGENT BEHAVIOR 

fingers and wrist so as to trace each letter in the proper way. 
This in turn is dependent upon our abiUty to hold a pen or 
pencil properly. After we have learned to form the letters 
by means of certain wrist and finger movements we extend 
the act to other muscles, as when we write large upon the 
blackboard. Again, certain elements in the act of writing 
are utilized when we learn typewriting or typesetting, while 
other elements used in handwriting are lacking in both of these 
acts. Owing to the intricate interconnection of the various 
brain centers in man an almost infinite number of such new 
combinations are possible. These new manifestations are not 
due merely to differences in the stimuli, as in the case of in- 
stinct, but they constitute new centrally determined modes 
of behavior. 

Significance of Intelligence. — When a motor habit is 
firmly established the act is often carried out with quite as 
much ease and precision as an instinctive act. On this account 
fixed habits are sometimes regarded as instances of * lapsed ' 
intelligence. According to this view the essential feature of 
intelligence is the acquisition of a new motor response, adapted 
to the situation. 

There is another reason why fixed habits are sometimes 
regarded as lapsed intelligence. Intelligence is popularly sup- 
posed to depend on consciousness to guide and direct the re- 
sponsive impulse into appropriate channels. But adaptive re- 
sponses sometimes begin in a purely accidental way; in other 
cases an individual modification of behavior may be started 
by ' social imitation ' of the actions of another being. Both 
of these types are intelligent acquisitions: yet they do not 
depend upon a " guiding activity of consciousness " operat- 
ing apart from neural processes. Even in the higher types of 
intelligence, such as rational actions, it is held by many 
psychologists that the thought processes which precede the 
response are subjective manifestations of neural activity. 
^ See Appendix, "Subjective and Objective Phenomena," p. 413. 



1 



SIGNIFICANCE OF INTELLIGENCE 129 

We may accordingly reject the view that intelUgence con- 
sists essentially in our becoming aware that one mode of be- 
havior is suitable and another mode unsuitable. Fixed habits 
appear to be no less characteristic of intelligence than new 
acquisitions. Intelligence means the progressive adaptation 
of response to the conditions of the environment, by means 
of individual modifications. Fixation and acquisition are 
equally important factors in this process. 

An illustration of the practical working of intelligence is 
found in the act of dressing oneself in the morning. There 
are certain garments to be put on; some of them require a 
fixed order (stockings before shoes, etc.), in other cases the 
order is indifferent (shoes and shirt). If we have learned a 
fixed order of dressing we complete the act more quickly and 
with fewer useless movements. Again, each particular act 
of dressing involves specific movements, some of which are 
quite intricate. Even the simple act of buttoning the coat 
involves a complicated adjustment of muscular movements. 

The dressing process is not instinctive, but an individual 
adaptation. It is the result of a long and intricate learning 
process involving both acquisition and fixation. Without the 
high degree of fixation which we have gained through frequent 
repetition the very first item in our day's program would be- 
come an Herculean task. The fixation of movements, instead 
of indicating a lapse of intelligence, is really essential to the 
highest degree of intelligence and adaptive behavior. 

There is a wide-spread popular notion that habits are bad 
things and should be avoided. We are continually warned 
not to get into a rut. Like most popular generalizations, this 
is partly true, partly false. Habits are useful and indispen- 
sable insofar as they fit us for coping with the conditions of 
life and in that they form the basis of more complex acqui- 
sitions. They are detrimental and undesirable when they 
become so firmly fixed as to prevent us from adapting our 
behavior to new conditions. 



130 INTELLIGENT BEHAVIOR 

If we are so wedded to smoking that we waste valuable time 
at important junctures, or if we are so fond of telling anec- 
dotes that we cannot readily adopt the role of listener, we are 
likely at times to lose certain business or social advantages. 
Almost everyone develops certain mannerisms and actions 
which in a minor way waste time and energy, or which are 
disturbing to others. Nervous movements, drumming with 
the fingers or tapping with the foot, hemming, coughing, and 
giggling are useless habits; a shrill tone of voice, uncouth 
table manners, whistling in public, and the like are socially 
annoying. All these may be classed as *bad habits.' Still 
worse from a biological and psychological standpoint are 
such habits as intoxication or the use of drugs, which impair 
the vital processes and weaken the mental life. 

While a distinction may be drawn between useful and detri- 
mental habits, it seems impracticable to classify intelligent be- 
havior under a number of general heads such as were found 
in the case of reflexes and instincts. An intelligent act, un- 
less it be of a simple type, involves many neural paths and 
a variety of terminal organs ; it usually serves to promote the 
general mental life of the individual and is not readily identi- 
fied with any one specific vital function. Even the distinc- 
tion between social acts, acts directed toward individual 
welfare, and acts concerned with the general physical environ- 
ment is unsatisfactory; for in most human activities more than 
one of these factors is involved. 

The difficulty of classification serves to emphasize the fact 
that intelligent behavior represents a response to the entire 
situation which confronts a creature, rather than a reaction 
to specific stimuli. Intelligence in its higher manifestations 
tends to express the organism as a whole, not merely some 
specific phase of organization. 

In the complex types of intelligent behavior the all-impor- 
tant factor is central adjustment. The operation of adjust- 
ment is open to a new method of investigation. The method 



SIGNIFICANCE OF INTELLIGENCE 131 

of self-observation enables us to examine the central processes 
as ' mental states.' This study furnishes a far more charac- 
teristic view of intelligence than the behavior method. Be- 
ginning with the next chapter we shall examine the central 
'phenomena of intelligent mental life as observed in our own 
individual experience. 

Summary of Chapters V to VII. — Psychology deals with the 
interrelations between the organism and its environment which 
are brought about by the passage of impulses through arcs of 
the neuro- terminal system. The activity occurs in three suc- 
cessive stages, called stimulation, adjustment, and response; 
each of these depends upon the operation of one of the three 
segments of the arc (ch. v). 

The operation of the entire neuro-terminal arc constitutes 
behavior. There are three distinct types of behavior : reflex, 
instinctive, and intelligent. 

Reflex behavior is due to the formation of certain fixed and 
definite pathways in the neurons which constitute lines of least 
resistance to the passage of impulses. These pathways are 
determined by inherited configurations of nerve structure. 
In reflex action the stimulus excites a sensory impulse which 
leads directly through a center or series of centers to a motor 
path and thence to a muscle or gland, resulting in some defi- 
nite response. 

Instinctive behavior consists in a complication of reflexes 
which results in a complex response; it usually involves a series 
or chain of responses. The formation of pathways for the 
impulses concerned in instinctive behavior depends upon in- 
herited nerve structure. Human behavior is rarely of the 
purely instinctive type, but it includes many modified instincts 
and instinctive tendencies (ch. vi). 

Intelligent behavior, like instinct, is a complex response or a 
series of responses resulting from the cooperation of several 
reflexes ; but in intelligence the lines of connection are not due 
to inherited structure; they are built up by individual experi- 



132 INTELLIGENT BEHAVIOR 

ence and perfected through repetition. The development of 
inteUigent types of response is called learning or habit-forma- 
tion; it involves the two factors of acquisition SLud fixation. 

Behavior in general is adapted — that is, the response tends 
to meet the conditions of the environmental situation which 
stimulates the creature. This fitness of response is apparently 
due to natural selection, which operates either in race history 
(instinct), or in individual experience (intelligence). (Ch. 
vii.) 

The central factors in intelligent mental life are open to 
investigation by the method of self-observation, and will be 
examined from this standpoint in the remainder of the book. 

Collateral Reading: 
Thorndike, E. L., Educational Psychology (briefer course), Part II. 
Parmelee, M., Science of Human Behavior, ch. 14. 
Judd, C. H., Psychology, General Introduction (2d ed.), ch. 9. 
Woodworth, R. S., Dynamic Psychology, chs. 4-6^ 
Watson, J. B., Behavior, chs. 6-8. 

Meyer, M., Fundamentals of Human Behavior, chs. 7-10. 
Mellone, H. S., Elements of Psychology, ch. 7. 
Swift, E. J., Mind in the Making, ch. 6. 
Colvin, S. S., The Learning Process, chs. 1-4. 

Rowe, S. H., Habit Formation and the Science of Teaching, chs. 3-5. 
Ebbinghaus, H., Memory (trans.). 

Practical Exercises : 

Test the formation of some new habit. [This should be assigned two 

weeks ahead.] 
Make a list of 'useless' and 'annoying' habits observed in those around 

you, including some of your own. 
Practice mirror-writing, looking in the mirror attentively and with your 

hand concealed. Report any notable feature of the experience. 



CHAPTER VIII 
CONSCIOUS EXPERIENCE 

The Method of Self-Observation and its Data. — So far we 
have considered mental life in terms of stimulation and 
response. These form the beginning and end of neural ac- 
tivity. Stimulation produces activity in the receptors and in 
the sensory segment of the nervous arc; response is the activity 
of the effectors determined by impulses in the motor nerves. 
The operation of stimulation and the operation of response 
are both open to scientific investigation by various ' objective 
methods.' The investigator can observe their phenomena 
readily in animals and human beings. 

At the present time we have no objective means of observ- 
ing the workings of the central neurons while integration and 
coordination are taking place. Physiology gives us little in- 
formation about these central operations, and behavior study 
is concerned with them only indirectly. 

Our objective knowledge of the activity of the central part 
of the arc is derived from a study of brain structure (espe- 
cially the topography of various centers, areas, regions, and the 
way the centers are connected together by association fibers), 
and from a study of the general properties of neural activity. 
We do not know the precise manner in which this activity 
operates, nor the means by which the passage of a current 
through a given synapse is facilitated at one time and in- 
hibited at another. These questions are not so important in 
the study of reflexes and instincts, where the action is fairly 
uniform; but our lack of knowledge of the central processes 
seriously hampers the study of intelligent behavior. 

The deficiency in the objective data is largely compensated 
for by our ability to examine the central processes as they 



134 CONSCIOUS EXPERIENCE 

occur in our own mental life. When certain nerve processes 
are going on in your own brain you are at the same time under- 
going certain dej&nite experiences; you see, you hear, you think, 
you are pained, you desire, you decide, etc. In other words, 
each one of us has what is sometimes called an inside view of 
the workings of his own neural processes. Since the terms 
' inner ' and ' outer ' are likely to suggest the distinction be- 
tween things inside and outside the body, it will be clearer to 
call an individual's self -observation of his mental life the sub- 
jective aspect of the central occurrences, and the observation 
of these same occurrences by another individual their objec- 
tive aspect. Or we may call the data subjective and objective 
phenomena respectively.^ 

Subjective phenomena differ radically in appearance from 
objective. Our perceptions, memories, etc., are quite different 
from nerve currents, light vibrations, muscle contractions, 
etc., which we investigate with physiological and physical 
instruments. The differential feature of subjective phenom- 
ena is denoted by the term consciousness. In other words, 
consciousness is defined as the distinctive characteristic of sub- 
jective mental life. Subjective phenomena are termed con- 
scious experiences. 

The study of conscious experience forms a distinct branch 
of psychological investigation. It adds much to our informa- 
tion regarding mental life obtained by the behavior method, 
since it deals with a class of phenomena which objective meth- 
ods at present can not reach. In human psychology the study 
of subjective phenomena by self-observation forms the larger 
part of the science; until quite recently it was supposed to 
embrace the entire field of psychology. 

Casual and Scientific Self-Observation. — Every normal 

human adult can observe and does observe his own conscious 

experiences. This fact often leads to the notion that one can 

readily become a psychologist without studying or training. 

^ See Appendix, "Subjective and Objective Phenomena," p. 413. 



SCIENTIFIC SELF-OBSERVATION 135 

The teacher of psychology constantly meets with this convic- 
tion among his students — especially when he reads the re- 
sults of written examinations. 

The fallacy here lies in the confusion of untrained observa- 
tion with scientific observation. The same confusion appears 
in other fields of science. One can observe physical and chem- 
ical phenomena as readily as he can observe his own mental 
phenomena. In either case an untrained observer is likely 
to misread or misjudge the facts. 

For ages it was assumed that a heavy body falls faster than 
a light body. Everyone observes objects fall to earth; the 
ancients (like the average man of to-day) took no trouble to 
observe the phenomenon accurately, and so the law of falling 
bodies was misstated until Galileo performed his crucial demon- 
stration. In the same way the ancients, observing the gross 
form of material things, concluded that there are four elements 
in nature: earth, air, fire, and water. This traditional view 
persisted till Cavendish, Priestley, Scheele, Lavoisier, and 
other trained chemists separated hydrogen, oxygen, and other 
elements from their compounds by means of crucial experi- 
ments and determined their relations. 

In psychology casual observation has given rise to a host of 
popular misinterpretations, some of which persist to-day. 
Almost everyone who has not studied mental life scientifically 
will assert that man has but five senses, with possibly a 
" mysterious sixth." The ancients regarded the heart as the 
seat of affection and the viscera as the seat of the powerful 
emotions. The average person is likely to think of his ' will ' 
or ' volition ' as a very simple phenomenon. 

All the popular notions just mentioned are erroneous. Man 
possesses at least ten or eleven distinct senses; the emotions 
and affections, like other mental phenomena, are centered in 
the brain; volition is a very complex process, involving high 
development of the brain centers. In order to obtain a true 
knowledge of psychological principles it is necessary at the 



136 CONSCIOUS EXPERIENCE 

outset for the student to rid himself of the conviction that his 
untrained observation of his own mental states is scientific 
psychology. 

Scientific psychology began in an attempt to reduce the 
results of uncritical self -observation to a system. Some slight 
progress in this direction was made by Aristotle, who classified 
the senses, noticed the illusion of the crossed fingers, examined 
memory and association, and collected a quantity of general 
data. The reduction of this material to a system dates from 
the investigations of Descartes, Hobbes, and their successors 
in the seventeenth and eighteenth centuries. In its earlier 
stages the scientific work in psychology was based almost 
entirely upon self-observation, or introspection, as it was 
called. This purely subjective line of research culminated 
with Thomas Brown's Philosophy of Human Mind in 1822. 
Brown consistently rejects every attempt to correlate con- 
scious experience with nerve activity. 

Even before this time, however, it had become more and 
more evident that the states and processes of conscious ex- 
perience are closely bound up with the activities of the nervous 
system, and during the past hundred years psychologists have 
come to recognize more and more the importance of studying 
the structure and functions of the brain. This led at first to 
the crude ' materialistic psychology ' of Priestley and to the 
phrenology of Gall and Spurzheim. The phrenologists as- 
sumed that certain mental functions, such as combativeness, 
amativeness, etc., are centered in various parts of the brain, 
and that their degree of development in any individual may 
be determined by measuring the protuberances in the skull 
overlying the several regions. 

The method of phrenology involves two errors: (1) The 
growth of the skull with its ' bumps ' and depressions does not 
correspond by any means to the development of the brain 
beneath. (2) The mental faculties assumed by the phrenolo- 
gists to be fundamental are now known to be highly complex 



SCIENTIFIC SELF-OBSERVATION 137 

processes; the elementary forms and characters of conscious 
experience are quite different from these. 

The development of scientific psychology based upon self- 
observation and neurology dates from David Hartley and 
James Mill; but the use of quantitative and experimental 
methods of research was not attempted on any large scale 
till later. Weber, Fechner, and Wundt are responsible for 
introducing these methods, which have made modern psy- 
chology a really quantitative science. 

Characters of Experience : Quality and Intensity. — The ex- 
periences of our daily life are very complex phenomena. The 
acts of thinking and willing are made up of simpler processes. 
Even relatively simple states, such as feeling, seeing, remem- 
bering, are the results of combining certain elementary data 
which never occur separately in adult human experience, 
though they may be isolated in the child and in lower ani- 
mals. Before examining the different kinds of conscious ex- 
periences, then, we must study the elementary factors and 
states which enter into their composition. 

The factors which determine the nature of specific experi- 
ences are of two sorts : 

(1) Conscious experience is determined by the nature of the 
stimuli which generate the nerve impulses. Variations in 
stimulation produce variations in consciousness. The inde- 
pendent kinds of variation brought about in this way may be 
called characters or attributes of experience. 

(2) Conscious experience is also determined by the nature 
of the neural processes. The fundamental operations of nerve 
(ch. iv) produce variations in consciousness, and corresponding 
to each of these neural properties is an operation or property ^ 
of conscious experience. 

The two statements may be combined in the following gen- 
eral law: The form of central activity and conscious experience 

1 Operation refers to the process, property is the capacity for change, or the 
type of effect resulting from the operation. 



138 CONSCIOUS EXPERIENCE 

depends both upon the action of the environment and upon the 
specific operations of nerve. 

The fundamental characters of conscious experience are 
quality and intensity. Quahty corresponds to the mode of the 
impulse, intensity to the intensity of the impulse. These neu- 
ral phenomena were discussed in chapter iv; the correspond- 
ing subjective phenomena will be examined later. ^ 

Fundamental Operations of Experience. — Apart from the 
variety introduced into conscious experience by differences 
of stimulation, our mental states are altered by conditions 
within the nervous system. Each of the properties of nerve 
noticed in chapter iv is also a property of conscious experi- 
ence. We may examine them again from this subjective 
standpoint. 

1. Impression. — Impression is the mental operation or 
property of conscious experience which corresponds to excita- 
tion of the neurons. When an impulse reaches the higher 
centers, the human being whose brain is concerned experiences 
something. He sees, hears, remembers, etc. The capacity to 
receive these conscious experiences is called impressibility ; 
the process is impression. Since all our observed experiences 
are due to activity in the cerebral cortex, impression can only 
be definitely assumed in connection with cortical activity. 
It is quite possible, however, that impressions occur also 
in the basal masses, cord, and sensory neurons. 

2. Suggestion (Successive Association). — Suggestion or 
successive association is the property of conscious experience 
which corresponds to conduction of the nerve impulse. As 
the impulse passes from one central neuron to another it fre- 
quently changes in mode owing to the retention set of each 
neuron through which it passes and to other impulses which 
reach the brain at approximately the same time. In terms of 
self-observation, one conscious experience gives place to an- 
other, through the revival of former impressions or the occur- 

^ See especially chs. ix-xii. 



SUGGESTION 139 

rence of new sensations. This succession of experiences is 
often called successive association or association of ideas. ^ 

The process of suggestion depends upon the progress of 
the nerve impulse in the central neurons. There are three 
possibilities: Either (1) the impulse may pass out into some 
motor channel; or (2) it may pass into some central neuron 
which is simultaneously affected by another impulse; or (3) it 
may pass into some neuron which has retained a set from pre- 
vious impressions. 

In the first case the result is expression; the nerve impulse 
in question has no further direct effect on conscious experi- 
ence. It may lead indirectly to another experience. The 
sight of a friend may start in us a motor impulse to wave 
our hand; this movement in turn causes a kinesthetic stim- 
ulus which leads to renewed central activity and con- 
sciousness. 

In the second case, where the impulse passes into a neuron 
affected by other impulses, the result is either a partial change 
in the form of experience or a complete change from one ex- 
perience to another. This is one type of suggestion. Our 
visual experiences when we look at a book are combined with 
our kinesthetic experiences when we lift it; or they pass over 
into something quite different when we look away from the 
book to the window. 

The third case, where the impulse passes into another 

neuron and is there transformed by the retention effect, is the 

typical form of suggestion found in human experience. In 

civilized man these suggestions constitute an important part 

of daily experience. A sensation or perception leads to a 

memory or a thought; this leads to another ideational process, 

and so on through a long chain of experiences. For example, 

^ These terms are open to misinterpretation. (1) In ordinary language 
'association' includes simultaneous combinations as well as successions, but 
the process we are considering is always succession. (2) The flow of ex- 
periences or stream of conscioxisness includes successive sensations as well 
as successive ideas. The term suggestion meets both these difficulties. 



140 CONSCIOUS EXPERIENCE 

I see the name of my former professor of history, this sug- 
gests the image of the man himself, his particular tone of voice, 
a phrase of his about Napoleon, the image of Napoleon, the 
French Revolution, the Russian Revolution, Tolstoi, etc. 
Unless the train of thought is interrupted by some new and 
potent stimulus it may proceed through one step after an- 
other for many minutes. The process of suggestion gives 
rise to the flow of thought, or in more general terms to the 
stream of consciousness (ch. xvi). 

3. Revival (Memory). — Revival is the property of con- 
scious experience which corresponds to the retention effect in 
the neurons. This operation is commonly called memory. 
The two terms may be used interchangeably provided we dis- 
tinguish between the simple memory experience and definite 
memory images. Revival or simple memory may occur with- 
out a definite memory image. It includes the bare ' feeling 
of familiarity ' ; it covers also experiences which have not even 
this tinge, but are unrecognized reproductions of earlier ex- 
periences. An example of revival in a highly developed form 
is my experience when I recall with vividness and precision the 
scene and incidents at my brother's wedding many years ago. 
A less vivid revival is the feeling of familiarity when I see an 
old friend or hear a well-known piece of music. Revival oc- 
curs in the lower species as well as man, but there is no evi- 
dence in the lower species of long trains of ideas, or even of 
vivid memory images such as we observe in ourselves. 

4. Vividness (Attention, Focalization). — Vividness is the 
property of conscious experience which corresponds to varia- 
tions in the metabolic condition of the synapses. Such va- 
riations serve to facilitate or inhibit the discharge of the 
nerve impulse into the central neurons. When a synapse is 
fatigued, but is not wholly impermeable, the impulse which 
passes through it is damped or lessened in volume. As a result, 
the experience itself becomes less effective; it decreases in 
vividness. If a synapse is in prime condition, the impulse 



VIVIDNESS 141 

passing across it retains its full vigor, with the result that the 
experience is unusually effective or vivid. 

This character is commonly called attention. The term 
attention, however, has several other meanings : it is used to 
denote the motor accompaniments of vivid experiences, as 
well as the degree of intellectual interest. which accompanies 
vividness. To avoid this ambiguity it is preferable to use the 
term vividness to denote the subjective accompaniment of 
metabolic variations. It may also be called focalization, since 
it renders certain portions of the total experience especially 
clear and prominent. 

We should distinguish between vividness variations and the 
variations in intensity of experiences which are due to the na- 
ture of the stimulus. Notice, for example, the effect of three 
noises, one very loud, one of moderate intensity, and one so 
soft as to be scarcely heard. If these are repeated under va- 
rying conditions of 'focalized attention,' we observe that the 
very faint sound is at times more vivid than the very loud. 

With stimuli of medium intensity all degrees of vividness 
may occur. When we listen to a lecture delivered in an ar- 
dinary tone of voice, certain phrases or sentences may be 
vividly impressed upon us, others may barely pass muster, 
while at times a train of thought may crowd the spoken words 
entirely " out of consciousness." 

With unusually powerful stimuli the very strength of the 
stimulus itself is apt to give great vividness to the experience. 
With very faint stimuli other processes are likely to prepon- 
derate, so that the experience in question is likely to have a 
low degree of vividness. But even where a very intense and 
a very faint stimulus occur together the experience of the lat- 
ter may be more vivid. It is said that the inhabitants of 
Niagara village scarcely hear the roar of the falls. Members 
of the New York Stock Exchange acquire great proficiency 
in picking out certain significant words from the babel of 
voices on the floor. 



142 CONSCIOUS EXPERIENCE 

5. Combination (Simultaneous Association). — Com- 
bination is the property which corresponds to the summation 
of nerve impulses. It usually happens that several stimuli 
act upon different receptors at the same time and the impulses 
which they excite reach the brain together. These separate 
impulses may be collected into one neuron. The result is 
a single complex impulse in the brain, and a complex impres- 
sion in conscious experience. 

There are two different sorts of combination: 

(a) Fusion, in which the elementary data are so merged that 
it is difficult to distinguish them. In fusion we experience a 
total effect, which is different from its separate parts. This 
is observed in the perception of a musical chord; the effect is 
apparently simple — we do not ordinarily pick out the con- 
stituent notes, although the practiced musician may do so, 

(6) Colligation, in which the elements remain distinct, 
although they are gathered together in a single experience.^ 
. Colligation occurs in our perception of colored surfaces, of the 
letters which make up a printed word, of the human face with 
its several features, etc. 

In general, simultaneous impressions in the sense of hear- 
ing tend to group themselves by fusion, while impressions in 
the sense of sight are grouped by colligation. 

Combination is sometimes called simultaneous association. 
The operation is quite different from successive association. 
In successive association certain elements of earlier experiences 
do hold over and combine with new elements in later experi- 
ences. This happens when we think of a door-knob and then 
of the door — the knob being an element in the latter 
thought. But the combining process takes place after the 
transition and is a distinct property of conscious experience. 
Combination is the ' synthetizing factor ' of consciousness. 
It is an important factor in building up complex experiences, 
such as perceptions, general ideas, etc. 

^ The terms integration and complication are also used for this process. 



DISCRIMINATION 143 

6. Discrimination. — Discrimination is the property which 
corresponds to distribution of the nerve impulse. An impulse 
may pass partly through one synapse, partly through another, 
giving rise simultaneously to different impulses in two or more 
neurons further on in the arc. This is apparently the basis 
of our conscious discrimination between parts of the same total 
experience. For example, though we ordinarily perceive the 
human face as a whole, we are able to pick out any single 
feature from the mass and focus it. The vividness of the dis- 
criminated feature depends upon metabolic conditions at the 
various distributing synapses; but the discrimination itself 
is due to the shunting of a certain part of the impulse into a 
separate pathway. Discrimination is the ' analyzing factor ' 
of consciousness. 

7. Transformation (' Mental Chemistry ')• — Transforma- 
tion is the property of experience which corresponds to the 
modification of the nerve impulse. It occurs in connection 
with revival and also in fusion and colligation. When we 
recall an event our recollection is usually tinged more or less 
with some present sensory experience; the quality of the im- 
pression is transformed accordingly. In cases of fusion some 
elements in the experience may neutralize others wholly or to a 
certain extent, so that the total resulting experience is not pre- 
cisely the sum of the constituent parts. The effect may be ob- 
served even in colligation. To the college student in his third 
year the campus and buildings ' look different ' from their 
impression when he first arrived in town as a freshman. Or 
if we observe the word cab, the impression we get from this 
combination of stimuli is something very different from the 
impression aroused by the separate letters, c, a, and b. In all 
such cases the combination is attended by a qualitative change 
or transformation ^ of the experience. 

Transformation is an important factor in mental life. It 

^ The terms mental synthesis and mental chemistry have been applied to this 
operation. 



144 CONSCIOUS EXPERIENCE 

may occur even in the simplest combinations of sensations. 
When we perceive an orange the sensory data of sight, touch, 
heft, and smell are modified by the memory of taste, and the 
quality of the whole experience is transformed to a certain ex- 
tent. When the present stimulus is weak and the retention 
effect is very strong the sensory experience is transformed into 
a memory image or an imagination. In complex experiences, 
such as a general idea or a thought, the original elements are 
still further transformed and it is difficult at times to deter- 
mine whether the thought has any basis whatever in sensation. 
Table VII gives a list of the fundamental operations of 
conscious experience. The corresponding neural operations 
are shown in the second column. The two sets may be re- 
garded as different ways of observing the same occurrences. 
These properties are not isolated or separate phenomena. 

Table VII. — Fundamental Operations of Conscious 
Experience 

Conscious Operation Neural Basis 

Impression (sensibility) Excitation 

Suggestion (successive association) Conduction 

Revival (memory) Retention 

Vividness (attention) Metabolic Variation 
Combination (simultaneous association) Summation 

Discrimination Distribution 

Transformation (mental chemistry) Modification 

They denote merely the different ways in which the material 
derived from stimulation may be varied. Each operation is 
an independent variable.^ In any given experience the ef- 
fect of all or most of them may be traced. 

Subconscious Experience. — It often happens that a stimu- 
lus produces no observed conscious efiFect at the time, yet later 
its effect is experienced as a revival ; or it may not be discrim- 
inated and yet it may alter the quality of conscious experi- 
ence. For example, we may not be aware of a clock striking 
the hour, but later we may recollect that it did strike and 
^ Except perhaps transformation. 



SUBCONSCIOUS EXPERIENCE 145 

often we can recall the exact number of strokes. Or, we 
may not be able to distinguish the length of two lines that are 
nearly equal, and yet we may ' guess ' the longer correctly 60 
times out of 100. This " consciousness which is not con- 
scious" is called subconsciousness. 

There are two distinct sorts of subconscious phenomena: 
(1) A central impulse, whether weak or strong, which is not 
connected up with the chain of central neurons whose activity 
constitutes our present personal experience. (2) An impulse 
whose degree of vividness is so slight that it falls " below the 
threshold " of sensation. We may call the former subordi- 
nate consciousness, and the latter subliminal consciousness. 

The older psychology was inclined to doubt the existence 
of subordinate consciousness or rather to deny that phenom- 
ena which are not subjectively observed may properly be 
treated by the ' introspective ' method. This objection was 
met by the discovery of cases in which the subordinate ma- 
terial is highly organized and yields a co-conscious personality. 
Certain hysterical patients have been found with two or more 
distinct, organized personalities. In one state. A, they appa- 
rently lose all connection with the experiences belonging to 
the other state, B. When personality B reappears the memo- 
ries, feelings, and attitudes which characterized this state on 
former occasions return and constitute the background of the 
individual's mental life (ch. xviii) . Each state is evidently 
an organization of conscious experiences; yet each may be 
wholly cut off from the organization of the other. 

It seems equally probable that the lower centers are capable 
of experiencing organized impressions. It may be assumed 
that the striking clock is actually heard, though not in rel- 
ation to our dominant conscious life, and that the nerve 
impulses concerned in our fixed habits constitute ' conscious 
experiences ' of subordinate centers, even though they fail 
to connect with our higher mental organization. 

A recent development of psychology started by Sigmund 



146 CONSCIOUS EXPERIENCE 

Freud goes to the other extreme, maintaining that all our con- 
scious experiences are controlled by our subconscious life. The 
mistake of this theory lies in assuming that our subordinate 
conscious experiences constitute a single, highly organized 
personality. The subordinate mental life of most individuals 
consists probably of a number of separate, partly organized 
experiences, which are utilized as material by the fully organ- 
ized mental life (' personality ') of the higher central areas. 

The notion. of subliminal consciousness, which is supported 
by such facts as the judgment of nearly equal lines, has given 
rise to another extreme view. Clairvoyants maintain that 
their subliminal impressions are capable of such intensification 
that they become vastly more vivid than experiences of super- 
liminal intensity. It is probable that in the hypnotic state 
impressions of subliminal intensity may be magnified at times 
in this way. The texture of blank sheets of paper may be 
discriminated by a hypnotized person so that he identifies one 
sheet as a photograph of A, another as a photograph of B. 
The general character of these phenomena, however, is open 
to serious question. 

Marginal Consciousness. — In any complex experience the 
component parts tend to assume different degrees of vividness. 
Usually a certain group of data are focalized, the remainder 
taper off into obscurity. Visual experiences afford a ready 
illustration of this. Objects at the center of vision are focused ; 
those at the periphery may be scarcely noticed. The same is 
true of every complex experience, even where various senses 
are combined. The obscure elements which enter into the 
experience are called the margin, fringe, or penumbra of con- 
sciousness; they form at times a background to the vivid, 
focalized consciousness, or give a distinctive timbre to the 
total experience. 

These terms are used somewhat figuratively; the marginal 
elements are not always situated side by side with the focal 
elements. The heaviness we observe in looking at an iron 



MARGINAL CONSCIOUSNESS 147 

crowbar is marginal, though we locahze it in the visual 
object. 

The marginal components often play as important a r6le in 
the experience as the vivid focus. We shall notice this par- 
ticularly in examining the attitudes which form the back- 
ground of mental life (ch. xvii). 

Hyperesthesia and Anesthesia. — In comparing the same 
individual's experiences at different times it is found that with 
the same intensity of stimulation the degree of total conscious- 
ness may vary considerably. At times every stimulus, even 
one below the usual threshold, yields a vivid experience. 
This is called a condition of hyperesthesia. At other times the 
threshold is raised far above the usual level, so that a stimulus 
of medium intensity yields no conscious experience whatever. 
This condition is called hypesthesia. The limiting case, where 
even the most intense stimulation of a given receptor yields 
no experience, is called anesthesia. 

These special conditions are brought about by physiological 
agents working upon the receptors or nerves. The applica- 
tion of certain drugs to the receptors produces local anesthesia. 
Narcotics introduced into the system produce general hypes- 
thesia or anesthesia. Stimulants similarly applied produce 
local and general hyperesthesia respectively. 

All such special conditions are the result of metabolic varia- 
tions in the neurons or receptors, brought about by unusual 
metabolic activities in the organism. These general physio- 
logical changes affect either the central neurons, or the sensory 
neurons, or the receptors. 

The peculiar phases of conscious experience which occur in 
sleep and hypnosis will be discussed later (ch. xvi) . 

Fundamental Types of Experience: Sensation and Idea- 
tion. — In the preceding sections we have examined the ele- 
mentary factors which affect conscious experience. These 
external forces and neural operations, working together in 
various ways, bring about various kinds of experiences. Cer- 



148 CONSCIOUS EXPERIENCE 

tain of these types have been referred to from time to time in 
our illustrations. We have spoken of sensation, perception, 
emotion, memory, and volition. These and other types will 
be examined presently. We shall find that they exhibit differ- 
ent degrees of complexity. Some types are more fundamental 
than others. 

The most fundamental division of conscious experience is 
into two distinct types, one of which is determined chiefly by 
forces outside the nervous system, the other by certain condi- 
tions within. The mode of the central impulse is determined 
(1) by the mode of the stimulus, (2) by the retention effect 
and other neural properties. There are two corresponding 
types of conscious experience, according as one or the other 
of these classes of factors predominates. They are termed 
sensation and ideation respectively. If the quality of the ex- 
perience be determined wholly by the stimulus, the experience 
is 'pure sensation'; if the quality be determined wholly by the 
retention effect, regardless of present stimulation, the experi- 
ence is ' pure ideation.' 

As a matter of fact no adult human experience is either 
purely sensational or ideational. When we are impressed 
by a stretch of white wall, a pervasive odor, a thundering noise, 
each of these experiences is almost entirely a sensation; yet 
each suggests to us some previous experience or is at least 
' colored ' by the general effect of our past life. On the other 
hand, a train of memories and ideas is almost wholly idea- 
tional; but it is always tinged by the organic sensations arid 
feelings present at the time, if not by stimuli from outside 
our body. This is shown, for example, by the radical differ- 
ence in the flow of thought according as we are depressed or 
elated. 

The distinction between sensation and ideation is highly 
significant in the study of mental life. Since psychology is 
concerned with the interrelations between the individual 
and his environment^ it is of prime importance to distinguish 



FUNDAMENTAL TYPES OF EXPERIENCE 149 

between impressions which originate outside of the neurons 
and impressions due to the condition of the central neurons 
themselves. An idea — that is, an impression whose mode is 
determined by the retention effect in the neurons — is related 
only indirectly to the present environmental or bodily condi- 
tions. 

The retention effect is always due to previous nerve im- 
pulses, and these are originally determined by the mode of 
stimulation. Hence every idea is based upon sensory expe- 
riences which have occurred in the past. It follows that 
sensation is the original and ideation the derivative type of 
experience. 

The entire group of sensations furnished by each sort of re- 
ceptor is called a sense. Thus the sensations resulting from 
stimulation of the eyes are grouped together and called. the 
sense of sight or vision; the sensations mediated by a certain 
kind of corpuscle in the skin constitute the sense of touch ; and 
so on. 

In the next two chapters we shall examine each of the senses 
separately, beginning with the sense of sight, which is the 
most highly developed sense in man and plays the most im- 
portant role in his mental life. 

Summary of Conscious Experience. — Conscious experience 
is the name given to phenomena of central nerve activity when 
observed directly by the being in whom this activity is oper- 
ating.^ The two characters of experience, quality and inten- 
sity, are determined primarily by the mode and intensity of 
the stimulus. The seven fundamental operations or properties 
of conscious experience correspond to the properties of nerve 

^ There are several other definitions of conscious experience, and other 
ways of interpreting the relation between conscious experiences and 'brain 
states ' besides the double-aspect view. For sake of simplicity the subject has 
been treated from this standpoint, with no reference to the 'philosophic ob- 
jections ' which have been urged against the interpretation. The reader 
should remember that the relation between 'subjective' and 'objective' 
phenomena is still a matter of hypothesis. (See Appendix, p. 413.) 



150 CONSCIOUS EXPERIENCE 

substance (Table VII). The fundamental types of experience 
are sensation and ideation, which depend respectively upon 
stimulation and central retention effect. Sensation is the 
original and ideation the derivative type of experience. 

Collateral Reading: 

Angell, J. R., Psychology, ch. 4. 

James, W., Psychology, chs. 11, 13, 15, 16. 

Titchener, E. B., Text-Book of Psychology, sees. 1-5. 

Wundt, W., Introduction to Psychology (trans.), chs. 1, 2. 

Breese, B. B., Psychology, chs. 12, 18. 

Judd, C. H., Psychology, General Introduction (2d ed.), ch. 6. 

Holt, E. B., Concept of Consciousness. 

Marshall, H. R., Consciousness. 

Spencer, H., Principles of Psychology, Part 1, ch. 7; and Vol. II, pp. 505 c-d. 

Freud, S., Psychopathology of Everyday Life (trans.). 

Practical Exercises: 

Analyze your 'total experience' at some moment, e.g., three minutes ago, 

noting especially (a) its variety, {b) grouping into objects, thoughts, 

acts, etc., (c) attention and inattention to various parts. 
Describe any experiences of anesthesia or hyperesthesia in your own recent 

life. 
Examine how finely you can distinguish between colors seen in different 

rooms at very different times; compare with discrimination of colors 

side by side (with black or white border between). 



CHAPTER IX 

THE SENSES 

In studying each sense the following phenomena will be 
examined: (1) Structure of the receptor, (2) Physiology of the 
receptor, (3) Nature of the stimuli, (4) Qualities of sensation, 
with other special phenomena of the sensory experience. 

1. Sight (Vision) 

Structure of the Eye. — The specific receptors for visual 
stimuli are the rods and cones in the retina of the eye. These 
are affected by light waves, and they are affected in different 
ways according to the intensity and mode of the stimulus. 
But broadly speaking the receptor organ for sight is the whole 
eyeball, together with the muscles which produce and regulate 
its movements.^ [Fig. 30.] 

The eye consists of a nearly spherical body. Its outer 
coating is a tough white substance called the sclerotic, which 
covers the entire eyeball excepting the extreme front sur- 
face. The front surface of the eyeball consists of a transpar- 
ent coat called the cornea. 

Inside the eyeball, slightly behind the cornea, is the lens, 
a transparent disk which is convex on both its front and back 
surfaces. The lens is held in place by a circular muscle, which 
also, in connection with an accessory muscle, serves to regu- 
late its shape. When the accommodation or ciliary muscles ^ 
contract, the lens bulges out; as these muscles relax the lens 
flattens. The interior of the eye behind the lens is filled with 
a tough, transparent, jelly-like substance called the vitreous 
body. The vitreous prevents the lens from slipping out of 

^ A model of the eye should be examined if possible. 
^ Anatomists generally use the latter term; physiologists call them accom- 
modation muscles, from their function. 



152 



SIGHT 



place. In front of the lens, between it and the cornea, is a 
transparent fluid called the aqueous humor. The fluid char- 
acter of the aqueous enables the lens to bulge and flatten 
without much effect on the general shape of the cornea. Im- 




CDtTUU 

nenits 



ty. The optto c^. 

Fig. 30. — Cross- Section of Eye 

Horizontal section through center of right eye viewed from above. Retina extends forward 
(toward lens) on each side as far as the notch. In left eye the optic nerve pierces the retina 
at the rifht of axis xy, [From Licldey, after Schaefer.l 



STRUCTURE OF THE EYE 



153 



mediately in front of the lens, between it and the aqueous, is 
another circular muscle called the iris, which cuts off the light 
rays entering from the side. The transparent opening in the 
center of the iris is called the pupil. 

Back of the vitreous, on the inner rear surface of the eye- 
ball, is the re/ma. [Fig. 31.] The retina is a net- work of cells 



Interior of eyeball; vitreous 




iVk.10' 



Exterior of eyeball; choroid coat 

Fig. 31. — Layers of the Retina 

Schematic drawing of layers from the vitreous (interior of eyeball) to the choroid coat 
Layers: (1) inner limiting membrane, next to vitreous; (2) layer of nerve fibers; (3) layer of 
nerve cells; (4) inner molecular layer; (5) inner nuclear layer; (6) outer molecular layer; (7) outer 
nuclear layer; (8) outer limiting membrane; (9) layer of rods (long, narrow) and cones (short, 
thick); (10) pigmen*^ cell layer. [Based on Piersol.] 



154 SIGHT 

and tissues of various sorts. It consists of ten distinguishable 
layers. The first of these (numbering from front to back) is 
a sort of retaining wall. The second layer consists of fibers 
of the optic nerve, which are distributed over the entire area 
of the retina. Beyond this (still toward the back of the eye) 
is a layer of nerve cells, and then several layers of cells and tis- 
sues which serve to temper the light and modify its intensity. 
The ninth layer consists of minute rods and cones which are 
peculiarly susceptible to stimulation by light. The tenth 
layer contains pigment cells which absorb any light which has 
escaped the intervening obstacles. 

The rods and cones consist of elongated bodies arranged 
side by side and crowded closely together. The cones are 
shorter and thicker than the rods and taper to a point at the 
extremity situated toward the back of the eye. (The names 
will serve to identify each in the figure.) The rods are from 
0.04 to 0.06 mm. in length, and from 0.002 to 0.004 mm. in 
diameter. The cones are from 0.03 to 0.04 mm. in length and 
from 0.004 to 0.006 mm. in diameter. At the central region of 
the retina only cones occur. Further out each cone is sur- 
rounded by a border of rods, while further still toward the 
edge of the retina (i.e., near the front of the eyeball) the cones 
become more rare and at the extreme periphery they are ab- 
sent altogether. 

Three points in connection with the retina should be par- 
ticularly noted. 

(1) Blind Spot: The optic nerve does not distribute its 
fibers on the outer surface of the eyeball in man or in other ver- 
tebrates. The whole mass of neurons pass through the outer 
coating at the back of the eye and are distributed about, form- 
ing the second layer of the retina. Consequently the light 
waves which penetrate into the eyeball pass among the optic 
nerve fibers and cells before reaching the rods and cones. 
The light waves do not affect the endings of these neurons 
directly; the terminals of the optic neurons are stimulated 




STRUCTURE OF THE EYE 155 

only by the rods and cones. The stimulus passes through the 
retina from the inner surface to the outer in the form of light 
waves, and passes back again from the outer surface to the in- 
ner in the form of a nerve impulse. In the place where the op- 
tic nerve breaks through into the eyeball, the retina is entirely 
lacking. This place is called the blind spot.^ [Fig. 32.] 

(2) Fovea: The center of the retina is directly behind the 
center of the pupil; a line joining them passes through the 
center of the lens and 
of the eyeball. The 
region about the cen- x 
ter of the retina has a 
yellowish tinge and is 
called the macula lutea. 
At one point in the Fig. 32. - Map of Blind S^ 

macula (near the cen- ^Hnd spot of the author's right eye. Drawn from 

ter) there is a deoreS- ^^° nearly identical records made in 1901 and 1902. 
, , F = fixation-point. 

sion in the retina, in 

which the cones are crowded together much more closely 
than elsewhere. The result of this crowding together is that 
our discrimination of space is finer here than elsewhere. 
This region from its shape is called the fovea centralis. It 
constitutes the point of clearest vision. 

(3) Periphery of Retina: The retina does not extend over 
the entire interior surface of the eyeball. It does not even 
extend as far front as the limits of the sclerotic. (The limits 
of the two may be compared in Fig. 30.) It is obvious that 
beyond a certain point the retina would have no use whatever, 
since the rays of light passing through the pupil (the opening in 
the iris) and lens reach only a limited portion of the inner sur- 
face; forward of this there is no retina. 

^ The blind spot of the right eye may be observed by turning the page 
upside down. Hold book six inches from the face, close the left eye and 
with the right fixate the word ' It ' in the middle of the first line on page 
154. Move the book slowly nearer and farther away, keeping the same 
fixation. The page number will disappear and reappear. 



156 



SIGHT 



The two eyes not only cooperate, but in several ways they 
supplement each other. Our ability to estimate how far off 
an object is situated is due in part to binocular vision. Fur- 
thermore, the optic nerve breaks through the retina at differ- 
ent points in the two eyes, so that the blind spot of one eye cor- 
responds to a region of rods and cones in the other, and no 
point in the field before us is lost. 

Turning now to the motor mechanism of the eye. [Fig. 33.] 
The eye is held in place and moved by six muscles arranged in 



Opaning/e 

l«; OfiKOMerok, « 

a Man. >iMa cii>i>«.rai«6i\,,v, 




Fig. 33. — Eyeball and Muscles 

Right eye from right side; external rectus muscle in central foreground. [From Smith and 

Elder.] 



three pairs. One pair produce movements of the eye from 
side to side. These two muscles are called the internal 
rectus and external rectus. (The internal muscle is on the nasal 
side.) A second pair cause movements up and down. These 
are the superior rectus and inferior rectus muscles. The third 
pair pass obliquely across the eyeball, one above, the other 
beneath; they are called the superior oblique and inferior 
oblique. The oblique muscles assist in the up and down 



I 



STRUCTURE OF THE EYE 157 

movements/ and when two of the rectus muscles are working 
together the obhques hold the eyeball in position and prevent 
it from twisting circularly like the hands of a clock (torsion) . 
» Physiology of the Eye. — The operation of the different 
parts of the eye has already been noted. We shall consider 
the process of visual stimulation as a whole. The rays of 
light which strike the eyeball further than about 4 mm. from 
the center of the pupil are cut off by the sclerotic and iris; 
when the iris is contracted even more of the rays are cut off. 
Only those rays which strike the pupil opening pass through 
into the interior of the eye. These light waves pass first 
through the cornea, then through the aqueous, the lens, the 
vitreous, and finally through the several layers of the retina 
till they reach the rods and cones and stimulate them. The 
stimulation is believed to be a chemical process. 




Fig. 34. — Focusing of Objects on Retina 

When lens of the eye (L) is properly accommodated for the distance of a stimulus S which 
we are observing, all the light rays from S meet at a single point R on the retina. So for stimuli 
from other points above, below, to right, and to left of S, at the same distance. An inverted 
image of the object is thus focused clearly on the retina. 

Owing to the convexity of the lens the rays are bent as they 
pass through it. The shape of the lens is regulated by the 
ciliary muscle, so that under normal conditions all the rays 
from any given point in the field meet upon a single point in 
the retina. [Fig. 34.] Thus when the ciliary muscle is prop- 
erly adjusted each point in the surface or field which we are 

^ The recti do not pull the eyeball directly up and down, but if acting alone 
would turn it somewhat inward as well. 



158 SIGHT 

looking at furnishes a uniform homogeneous stimulus to one 
single point of the retina, so that the whole field of vision is 
clear and distinct. The projection of the objective field on 
the retina is upside down (inverted) like the picture on a 
photographic plate. 

The nerve fibers are excited by the activity stimulated in 
the rods and cones. The resulting nerve impulses are trans- 
mitted separately along the fibers, which are grouped together 
into a bundle called the optic nerve. The optic nerve passes 
through the blind-spot opening of each eye, and the two optic 
nerves come together a short distance beyond this; their junc- 
ture is called the optic chiasm. Here the fibers from the inner 
(nasal) half of each retina cross over, while those from the 
outer half proceed along on the same side of the head. [Fig. 
35.) It thus comes about that all the fibers from the left haK 
of both retinas pass to a visual center in the left side of the 
cerebrum and those from the right half to a center on the 
right side. 

Ciliary and Iris Reflexes. — If we look suddenly from near 
by to a greater distance, objects will be out of focus and 
will appear blurred; but the ciliary muscle immediately re- 
laxes and a sharp impression is at once obtained. This ad- 
justment is called accommodation, or uniocular focusing. When 
we look nearer, the ciliary muscle contracts, the lens bulges 
out, and the impression again is clear and sharp. In the 
normal eye the accommodation adjustment covers a range 
of distances from about 10 cm. (near point) to about 6 m. 
(far point) from the eye. 

When the general illumination of the field is suddenly 
brightened the iris muscle begins to slowly contract; as it 
squeezes together the pupil becomes smaller, the amount of 
light admitted to the eye is decreased, and after a period the 
dazzling effect disappears. Similarly, when the field is dark- 
ened the iris muscle gradually relaxes, the pupil is enlarged, and 
objects begin slowly to appear in the twilight. This adjust- 




Fig. 35. — Course of Optic Nerve 

Showing juncture of the two optic nerves at chiasm, with crossed and uncrossed fibers, and 
their paths beyond. 

E = eyeball; ON = optic nerve; CF = crossed fibers; UF = uncrossed fibers; OC = optic 
chiasm; OT = optic tract; GC = commissure of Gudden; P = pulvinar; EG = external ge- 
niculate body; IG = internal geniculate body; UQ = upper quadrigeminal body; N3, N4, 
N5 = nuclei of III, IV, V cranial nerves; C = cortex, occipital lobe. tModified after Lickley.j 



160 SIGHT 

ment is called the pupillary reflex or iris adaptation. It pre- 
vents injury of the retina through too intense stimulation. 

Eye Movements. — The ciliary and iris reflexes are motor 
processes which assist in visual reception. The movement 
of the eyeball as a whole is another motor process which regu- 
lates visual sensation. We noticed that the retinal elements 
are crowded closely together at the fovea, so that space dis- 
crimination is more acute. Objects are observed more pre- 
cisely when they lie directly in front of the fovea. 

By an inherited reflex mechanism the eye muscles act so that 
when the rays from a bright object (or an object especially ob- 
served) fall oij a point toward the edge of the retina the eye- 
ball quickly turns in such a way as to bring this object di- 
rectly in front of the center of vision. That is, the eye rotates 
till it ' centers ' the object on the retina. This centering of an 
object is called fixation. If the point to be fixated lies below 
the center, the inferior muscles of both eyes are contracted; 
if above, the superior muscles; if the point lies to the right or 
left the external muscle of one eye and the internal of the other 
are contracted. If the object lies diagonally above and to 
the right, both the superior and external muscles of the right 
eye are contracted, and the superior and internal muscles of 
the left eye; and so for other diagonal positions. 

In ordinary eye movements the superior muscles of the two 
eyes work together and so do the inferior muscles; the external 
muscle of one eye works with the internal of the other. But 
when we fixate from a point near the eye to a point farther 
away along the same line of regard, the external muscles of 
the two eyes work together, and conversely the two internal 
muscles when we alter our regard from a considerable distance 
to a point nearer by. The change of fixation from far to near 
(or the reverse) is called convergence or binocular focusing. 

\ Visual Stimuli. — The light waves which serve as stimuli for 
ight are minute vibrations in the ether." There are two dif- 
ferent types of physical vibration, longitudinal and transverse. 



VISUAL STIMULI 161 

Longitudinal waves are those in which the particles move 
forward and back in the same line of direction as the wave 
movement. In transverse waves the particles vibrate from 
right to left or up and down — that is, at right angles to the 
direction of propagation of the wave. The transverse type is 
illustrated by the surface-waves of a body of water when a 
stone is thrown in. The particles of water at any point move 
up and down as the wave passes, while the wave of disturb- 
ance moves horizontally away from the starting-point. Light 
waves belong to the transverse class, while sound waves are 
longitudinal. The distinction, though important in physics, 
is of no great moment for psychology. 

The ether waves form a series, extending from vibrations 
of very minute amplitude to those of very great amplitude. 
The long waves (those of great amplitude) do not affect the 
organ of sight. Some of these are classed as heat waVes and 
affect other senses. Similarly, the very short waves do not act 
upon the retina, though they are capable of producing chemi- 
cal effects on a photographic plate. The intermediate waves, 
from about 760 /a/a (millionths of a millimeter) to about 
390 fifx, act upon the rods and cones of the retina and serve as 
visual stimuli.^ 

When sunlight or any mixed light passes through a prism, 
the waves are refracted. Short waves are bent more than 
long waves. If the waves after passing through the prism 
be projected upon a white surface the whole series is distrib- 
uted over the surface so that each wave length falls on a dif- 
ferent spot. [Fig. 36.] This orderly series of waves is called 
the color spectrum. The instrument for refracting and pro- 
jecting is called a spectroscope. 

AU ether waves travel through the atmosphere at the rate 

of about 300,000 kilometers (i.e., 200,000 miles) per second. In 

any medium of given density a light wave travels always at 

the same speed, regardless of its wave length or intensity. 

^ The exact limits are difficult to determine. 



162 SIGHT 

In other words, the speed of transmission is not a variable 
factor. But the number of waves which reach a given point 
in a given period of time is a variable factor : it varies inversely 
with the wave length. Thus the length of the light wave 
which gives the bright line B in the solar spectrum (a certain 




Fig. 36. — Refraction of Light 

Mixed waves (traveling from left to right) are refracted at each surface of the prism; the 
shortest waves (violet end of spectrum) are bent most, long waves (red end) least. At any re- 
flecting plane beyond the prism they form a spectrum. 

red) is 687 /x/x; 417 trillion such waves strike the retina every 
second. Toward the other limit, the wave length of the G line 
(a certain violet) is 432 /^/x; 693 trillion such waves strike the 
retina per second. 

Either the variations in wave length or the number of waves 
per second may be used as basis for measuring the vibration 
rate of the stimulus. These differences in light waves give rise 
to various modes of impulse in the optic nerve, and when the 
effect reaches the brain they produce different qualities of 
visual sensation. Each distinguishable color is caused by a 
specific rate (or range of rates) of light vibration. The so- 
called pure or white light observed in ordinary sunlight is a 
mixture of waves of all rates of vibrations. When no particu- 
lar rate preponderates, mixed light waves give rise to the sen- 
sation of gray or white. 

In addition to their differences in wave length, light waves 
may vary in intensity or amplitude of swing. An intense 
wave is one in which the particles are impelled with greater 
force and consequently vibrate further from side to side. An 
intense light wave acts more powerfully upon the rods and 



VISUAL STIMULI 163 

cones than a less intense wave, resulting in a sensation of 
greater intensity. The phenomenon of intensity is observed 
centrally as degree of brightness in the sensation. An intense 
physical light wave causes a bright visual sensation; a wave 
of low intensity gives rise to a faint or dim sensation. 

Quality and intensity are the two variables in the stimulus 
which determine the two chief characters of a sensation. 
Physical light waves vary also in duration and extensity. 
Both of these differences are observed by the human subject, 
but they are characters of sensation groups rather than of 
individual sensations, and are more appropriately discussed 
under the head of perception. 

Characters of Visual Sensation : Qualities. — The quali- 
ties of visual sensation consist of two independently varying 
groups or series: (1) A series of color hues whose stimuli are 
waves of one single rate, and (2) a series of grays, whose stim- 
uli are waves of many different rates combined. The gray 
series includes all shades of brightness; its extremes are the 
two sensation qualities called black and white. 

The color qualities and the gray qualities may be combined 
in one sensation; this occurs when a stimulus consisting of 
a light wave of some definite length is accompanied by stimuli 
consisting of a general mixture of waves. Such combinations 
may occur in various proportions. For any given color a 
graded series of sensations may be obtained by increasing 
or decreasing the proportion of mixed light waves to single 
wave rate in the stimulus. This gives a third series called the 
series of tints. ^ 

a. The Color Series ; HUes. — Each pure color is due to 
stimulation of the retina by light waves of one single, definite 
length. Light waves form a continuous series, so that there 
are an infinite number of different physical wave lengths 
within the limits capable of stimulating the retina. But we 
do not distinguish an infinite number of colors. The sensa- 

^ Also a fourth series called color-shades, as will be explained presently. 



164 



SIGHT 




tion produced by a 400 [ifx. wave is not observably different 
from the sensation produced by 410 /x/a. Each observably dif- 
ferent color is called a hue or color tone. The number of no- 
ticeably different pure color qualities may be determined by 
observing two spectra, one above the other, or by color 
mixing. 

Color mixtures are made by interlocking two or more 
colored disks, so that each occupies part of the front surface, 
and placing them on the axis of a wheel (color mixer), which 

is rotated very rapidly. 
[Fig. 37.] This gives an 
impression of one single 
color over the entire area; 
it is intermediate between 
the two hues. 

To determine the hue 
which is just perceptibly 
different from the extreme 
red, we place a large disk 
of this red on the color 
wheel and over it place two 
smaller interlocked disks, 
one of the same red, the other yellow. Since the larger disk 
projects beyond the interlocked disks it can readily be com- 
pared with the mixture effect of the latter when the wheel 
is rotated. The proportion of the smaller disks is varied 
until the mixture is just perceptibly yellower than the larger 
standard disk. This procedure is continued, changing the 
colors used as need be, till we reach the other end of the spec- 
tral series (violet). We have then determined the number of 
perceptibly different color tones in the spectrum. 

This does not exhaust the series of color qualities. If we 
mix violet light with red in various proportions, we obtain a 
certain number of new color qualities, which are known as 
purples. These purple hues are entirely different from any of 



Fig. 37. — Color Mixer 

Color disks are placed on axis of wheel 4. The 
mixer is rotated by turning a handle on circum- 
ference of wheel 1. By a series of belts connecting 
wheels 1, 2, 3, 4, the speed of rotation is greatly 
increased. [From Judd, after Rothc] 



THE COLOR SERIES; HUES 



165 



the hues which appear in the spectrum. Including the group 
of purples, the color series consists of about 150 to 160 distin- 
guishable hues. The number varies in different individuals. 
The pure color series is called the scale of hues. It extends 
from red, produced by the longest wave, to violet, produced by 
the shortest, the two ends being connected by the purples, 
so that the whole constitutes a circular series. [Cf . Fig. 39 B.] 
Not all of the distinguishable hues have received separate 
names. The popular terms red, yellow, etc., apply to groups 
of similar hues. Primitive man seems to have distinguished 
four such color groups, red, yellow, green, and blue. This 
is indicated by the fact that these names are so ancient that 
all trace of their etymological origin has been lost. Somewhat 
more recently certain immediate groups (orange, violet, etc.) 
have received distinct names derived from certain common 
fruits, flowers, etc. The spectral range of the best recognized 
groups is given in Table VIII. 

Table VIII. — Spectral Lines and Color Range 



Spectral Line 


Wave Length 


No. of Vibrations 
Trillion per second 


Color 
Hue 


Range 


A 


766.1 




391.41 






Primal Red 












B 

C 


687.0 
656.28 




417.06 ) 
456.91 ) 


Red 


760-647 


D2 


589.0 




509.01 


Orange 


647-588 


Primal Yellow 


577 




521 


Yellow 


588-550 


E 
Primal Green 


526.96 
501 




569.03) 
599 ) 


Green 


550-492 


F 
Primal Blue 


486.14 

477 




616.82 ( 
629 f 


Blue 


492-455 


H 


432.58 
396.84 




693.19 ) 
755.62 ( 


Violet 


455-390 



Visible Range: 760-390 ji-H, 399.55-768.87 trillion. 

Limits of Color Change : 655-430 jji|x. 

(Wave lengths from Houston, Treatise on Light, p. 473. Slightly different 
values are given in older tables, based on a less accurate correction factor. 
Primal colors from Titchener, Exper. Psychol, Vol. I, Part I, p. 4. In many 
works the vibration numbers are given as "billions," following an old nota- 
tion. There are twelve places after the decimal point.) 



166 SIGHT 

The average educated man of to-day uses only eight or nine 
names for pure color distinctions. These are (in serial order) 
red, orange, yellow, olive, green, peacock (or blue-green), blue, 
violet, and purple. The purple group is sometimes divided 
into carmine and magenta. Distinctions within any color 
group are designated by compound names (yellowish orange, 
reddish orange, etc.). Technical names have been coined 
for certain specific hues, but they are not frequently used 
except by painters and other specialists. The name hrown 
is given to a group of impure yellows which are observed more 
frequently in nature than pure yellow itself. Other more or 
less familiar color names, such as maroon, baby blue, pink, 
etc., have been given to certain impure colors — either very 
light or very dark or highly tinted (unsaturated) colors. 

Certain color hues appear to be more fundamental than 
others. Orange resembles red, but red and green are wholly 
dissimilar. The number of fundamental colors and the exact 
hue which is fundamental in each case have been subject to 
much discussion. Isaac Newton, following the analogy of the 
musical scale, selected seven colors which he called primary : 
red, orange, yellow, green, blue, indigo, and violet. Later, 
Thomas Young and Hermann von Helmholtz developed a 
visual theory based upon three fundamental colors, red, green, 
and blue (or violet). The selection was due to the fact that 
these colors, when combined in various proportions, will pro- 
duce every other hue. ^ More recently Ewald Hering proposed 
a theory which recognizes four jyrimal colors which are specific 
hues of blue, green, yellow, and red. This four-fold scheme 
seems to accord better with our observation of the ' obviously 
dissimilar ' colors. It is further supported by the following 
experimental evidence: 

If the eye be fixated upon a point directly in front, and a 
color be moved gradually from near the fixation point out 
toward the periphery of the visual field, after a certain dis- 
^ See Appendix, "The Visual Process," p. 441. 



THE COLOR SERIES; HUES 167 

tance the color changes to gray. For most colors, as the 
stimulus is moved toward the periphery the hue alters some- 
what before passing into gray.^ Thus a color which appears 
green when observed directly may become slightly yellowish 
or slightly bluish as it passes into the indirect field. But 
there are four specific hues which do not alter except as they 
gradually become gray. They are blue = 477 /u,/a, green 
= 501 /A/x, yellow = 577 fxjx, and a slightly purplish red. These 
' invariable ' hues are the four primal colors. 

b. The Gray Series; Shades. — Besides the series of color 
hues we observe a series of colorless visual qualities known as 
gray. These extend from the sensation of pure white to the 
sensation of black. The series is not circular like the colors; 
the two limits are extremely different, and there is but one 
way of passing gradually from black to white if we rule out 
color impressions altogether. By selecting a medium shade 
of gray and comparing it with a variable gray stimulus, we 
can determine how much black or white must be added in or- 
der to get an effect just noticeably different from our stand- 
ard. The comparisons are continued in both directions until 
we reach the limiting white on the one hand and the limiting 
black on the other. About 700 shades of gray are distin- 
guishable by the normal human eye. 

While the gradations of gray are really due to differences of 
illumination, the sensation is accompanied by a qualitative 
change. It is not easy to recognize a quality difference be- 
tween two neighboring shades of gray; but if we compare 
samples of gray near the two extremes of black and white the 
difference of quality is very noticeable. 

Moreover, if a portion of the eye be stimulated for some 
time by white while the surrounding field is dark, and if the 
eye be then suddenly closed, it is found that the relations of 
the two portions of the field are reversed — what was white be- 
comes black and the surrounding black becomes white. This 
^ An apparatus used in this experiment is shown in Fig. 40, p. 177. 



168 SIGHT 

' complementary ' phenomenon (which appears in colors also) 
indicates that black and white are actually visual qualities. 

The gray series is called the scale of shades or brightnesses ; 
it constitutes an independent series from hues or color tones. ^ 

A diflSculty in explaining the gray series lies in the fact that 
black is not the result of any light stimulus at all; physically, 
it corresponds to absence of stimulation. Some psychologists 
seek to explain the phenomenon of black, which is a real sen- 
sation, by assuming that it is not due to any process in the 
retina, but to a process that takes place in the visual center 
of the brain. More probably, however, black is the result of 
a physiological process in the retina induced by actual stim- 
ulation by white in neighboring portions of the field. 

c. Mixed Series; Color-Shades and Tints. — The various 
shades of gray may be combined with the various pure color 
tones. This gives rise to a vast number of new visual sensa- 
tions. If we mix a pure red with a sector of white on the color 
mixer the result is a light or whitish red; if we mix the same 
red with a black sector we get a darker red. Both are 
variations in the shade of the hue. A graduated series from 
light red to dark red may be obtained by using the disk 
shown in Fig. 38 A. It forms the color-shade series for red. 
There is a color-shade series for each hue. 

Now suppose we select a gray disk which is neither brighter 
nor darker than the pure red disk we are using and rotate the 
two on the color mixer. What is the result? We observe that 
the color does not become either brighter or darker.^ But 

^ The division of visual impressions into a 'black-white' series and a 
'color hue' series is based upon variations of the stimuli, not upon observed 
similarities and differences among experiences. Self-observation gives 
several alternative classifications. In heraldry, for example, yellow and 
white are grouped together as 'metals'; red, green, blue, and black are 
'colors.' In popular anthropology the 'white' race is distinguished from the 
'colored' races, which include yellow, red, and black. 

^ If we find that it has become darker this means that the gray selected 
is darker than our red; the error can be corrected by choosing a lighter gray 
or adding a little white. 



COLOR-SHADES AND TINTS 



169 




Fig. 38. — Variations in Color-Shade and Tint 

A. Color-shade series. — Disk for demonstrating gradual change from light red at circumleh 
ence to dark red at center. 

B. Tint series. — Disk for demonstrating gradual change from pure, saturated red at circum- 
ference to very unsaturated red ending in colorless gray at center. fRed is represented in both 
figures by the dotted surface.) 



170 SIGHT 

the visual sensation is decidedly different from that of the 
* pure red.' The proportion between color value and gray 
value in the mixture is different. It is not a change in color 
hue nor a change in color-shade, but a third mode of color 
variation, called tint,^ chroma, or saturation. 

Whatever color we select, and whether its shade be light, 
dark, or medium, it is possible to add to it a certain gray of the 
same shade which will make it less saturated (less colored) 
without change of hue or shade. A graduated series of tints 
may be determined for any hue, beginning with the pure or 
saturated color and proceeding by least perceptible differences 
until we reach colorless gray. [Fig. 38 B.] 

For simplicity we have supposed that the gray and the 
colors are of the same brightness; but it is possible to mix a 
color of one shade with a gray of quite a different shade — 
very much brighter or very much darker. There will then be 
a change of both color-shade and tint. 

Number of Qualities ; Color Spindle. — The total number 
of different visual sensations is determined by combining the 
number of pure hues, the number of gray-shades, and the 
average number of distinguishable color-shades and tints for 
a single hue. But if we multiply these factors together the 
product is too large. Very light and very dark hues have 
much fewer tints than the pure spectral hues ; and at the ex- 
treme of brightness and darkness there is no variety of tint 
whatever — only white and black. It has been estimated that 
there are about 30,000 distinguishable visual qualities. 

Since three independent variables ^ (hue, shade, and tint) 
enter into the production of visual sensations, the relations of 
the different qualities to one another must be represented 
graphically in three dimensions. The relations are shown 

^ The term tint is used by some writers to denote bright shades of a color 
hue. 

2 Gray-shade may be treated as the hmiting case of color-shade — when 
the color value is reduced to zero. 



NUMBER OF QUALITIES; COLOR SPINDLE 171 



Vhrte 




Glade 



Fig. 39. — Color Spindle and Color Belt 

A. Color spindle; showing schematically the various distin- 
guishable visual sensations, arranged according to shade (ver- 

y-Colo' tical directions), tint (radii from central axis) and hue (angles 

Belt about axis). Gray series is represented by the central vertical 

axis. The purest hues (most saturated color tones) lie on cir- 
cumference of the color belt. Relative proportion of shades, 
tints, and hues is indicated by relative number of units as- 
signed to each. (Notice the preponderance of shade-units over 
others.) 

B. Color belt, enlarged; showing relative number of distin- 
guishable hues of each spectral color and of purple; relative 
saturation of the various pure hues is indicated by distances 
from central gray axis. 

(The angle assigned in the figure to each color in the belt 
is somewhat conjectural; border-line hues might be classed 
under either component. The curve of the color belt is also 
schematic; exact data are not available. The proportion be- 
tween circumference of belt and length of axis is fairly exact. 
The tilt of the belt in Fig. 39 A is indicated approximately.) 



in Fig. 39 A. The schematic representation 
of visual quahties is usually called a color 
pyramid, but on account of the great length 
of the axis it is more properly termed a color 
spindle. 

The series of colorless grays form the axis 
of the spindle, white lying at one extreme and 
black at the other. The pure colors, includ- 
ing the spectral hues and purples, are repre- 



172 SIGHT - 

sented by a belt surrounding the gray axis and lying in a plane 
which cuts the axis near its midpoint, [Fig. 39 A, B.] The 
various tints of any given hue are represented along a line 
from the color belt to the axis, and the color-shades run paral- 
lel to the axis. The length of the axis is 700 units; the color 
belt is 150-160 units in circumference. The radii vary in 
length. 

The shape of the spindle has only been roughly determined 
at present. The following points should be noticed: (1) 
The color belt does not lie in a horizontal plane. Yellow is 
distinctly lighter than green; violet is darker than the other 
spectral hues. In other words, the spectral belt is tilted up- 
ward at the yellow region and downward at the violet. 

(2) The circumference is irregular in form. Violet and blue 
are the most saturated colors, then follow (in order) red, 
peacock, orange, green, and yellow. In other words, the cir- 
cumference of the color belt lies furthest from the axis at 
violet, nearer at blue, and so on to yellow. The purples, being 
obtainable only by mixture, are less saturated than the spec- 
tral hues, especially at the midpoint between red and violet. 
They are represented in the color belt by a straight line. 

(3) At the two ends of the axis the color differences fade 
away completely, so that the spindle tapers down to a point. 
The white end of the spindle is somewhat sharper than the 
black. 

Every distinguishable visual impression, excepting those on 
the very outer circumference of the spectral belt and at the 
two poles (black and white) may be obtained by mixing (in 
proper proportion) two stimuli which lie on opposite sides of 
it in the color spindle. No pure spectral hue can be perfectly 
reproduced by a mixture of other hues; the mixture is always 
less saturated. The mixture of red and green, for example, 
will fall nearer the axis of the spindle than spectral yellow. 

It is possible by combining spectral red, green, and violet 
in various proportions to reproduce any hue in almost its 



NUMBER OF QUALITIES: COLOR SPINDLE 173 

purest (most saturated) form. By adding extreme white or 
extreme black (one or both) to the mixture any shade and any 
tint may be obtained. Hence we find the general law : " Every 
shade of gray, and every hue in every possible shade and in 
nearly every tint, can be produced by mixing black, white, 
pure red, pure green, and pure violet in various propor- 
tions." ^ 

Certain additional relations are observed among visual 
qualities, which will be examined next. 

Purkinje Phenomenon ; Adaptation. — The relative bright- 
ness of different hues varies with the intensity of the stim- 
ulus. Under most conditions of illumination yellow is the 
brightest spectral color. If the illumination of the field be 
increased, yellow and red become brighter more rapidly than 
the other hues. On the other hand, if the illumination of the 
field be diminished, the hues which represent long waves 
darken more quickly than the short-wave colors. The dif- 
ference appears most strikingly if we compare blue and red. 
The same shade of blue which appears darker than a given red 
when the general field is bright, appears brighter than this 
red in a faintly illuminated field. This variability in relative 
brightness of color hues is called the Purkinje phenomenon, 
from the first discoverer. 

The Purkinje phenomenon is associated with adaptation 
to bright and dark general illumination. Part of the adapta- 
tion process is a result of the iris reflex. When the general 
field is bright, the iris muscle contracts, the opening or pupil 
becomes smaller, and less light is admitted. In faint illumi- 
nation the iris relaxes, enlarging the opening and admitting 
more light. 

In addition to this muscular adaptation, a change of condi- 
tion occurs in the retina with changes of general illumination. 
This is attributed to a substance in the retina called visual 
purple, which is affected by light. In bright illumination 
^ For most mixtures only three of these or fewer are required. 



174 SIGHT 

the visual purple is modified and produces slight differences 
in the color hue and greater differences in the brightness 
component. On this account the relations of colors, both 
as to hue and shade, vary in daylight and twilight. At the 
center of the retina (where no rods are present) this difference 
does not appear. 

Adaptation for specific hues occurs when the general field 
is tinged with that hue. This is observed if we put on colored 
glasses. With green spectacles the whole field at first appears 
tinged mth green. After a time this tinge disappears and the 
field appears normal, though certain hues are altered from 
their ordinary appearance, and red objects appear gray. 

Complementaries. — If a disk of yellow cardboard and a 
disk of blue be fitted together so as to give a circle half yellow, 
half blue, and this be rotated rapidly on a color mixer, the two 

Table IX. — Complementaby Colors 



Standard 


Wave Length 


Complementary 


Wave Length 


Relation of 


Color 




Cdlor 




Wave Lengths 


Red 


656.2 


Green-blue 


492.1 


1.334 


Orange 


607.7 


Blue 


489.7 


1.240 


Gold-yellow 


585.3 


Blue 


485.4 


1.206 


Gold-yellow 


573.9 


Blue 


482.1 


1.190 


Yellow 


567.1 


Indigo-blue 


464.5 


1.221 


YeUow 


564.4 


Indigo-blue 


461.8 


1.222 


Green-yellow 


563.6 


Violet 


433. 


1.301 



[From Ladd and Woodworth.] 

will neutralize each other wholly or in large part. If we select 
a certain specific hue of each and mix them in various propor- 
tions, we will at some point find a mixture in which no color 
effect whatever is observed; the disk appears as a plain gray 
surface. For a given yellow, one and only one blue can be 
found which yields this effect. This yellow and this blue are 
called complementaries. For every color hue in the series, in- 
cluding the purples, one and only one complementary exists. 
[Table IX.] Black and white are treated as complementa- 
ries for reasons that will appear presently. 



AFTER-SENSATIONS 175 

After-Sensations. — If we fixate the eye for some time upon 
a very bright color and then look quickly at a plain gray sur- 
face, the portion of the retinal field where the color appeared 
will give a sensation of complementary color. Thus if we 
fixate a bright blue circle the after-effect is a yellow circle 
surrounded by a faint tinge of blue. The same effect is ob- 
served if we close the eyes after observing a bright color. 
Such an after-effect is called an after-sensation.^ It is due to 
fatigue of the stimulated retinal area for the given color. 
White gives rise to a black after-sensation, and conversely; 
for this reason they are considered complementaries. The 
degree of brightness and the period of fixation necessary to 
obtain an after-sensation vary greatly among different indi- 
viduals. The vividness and duration of the phenomenon may 
be increased by practice. 

If a practiced observer fixate a bright blue circle and then 
look quickly away, he will notice that the sensation of blue 
continues for a short time (part of a second) on the given 
region of the retinal field before the complementary appears. 
This effect is called a positive after-sensation. The comple- 
mentary effect which follows is a negative after-sensation. 

With practiced observers and under very intense illumina- 
tion the negative after-sensation may last for many seconds. 
If the fixation on the gray surface be maintained without 
winking, the negative after-sensation fades slowly away and 
may be succeeded by a second positive after-sensation. Oc- 
casionally a second negative follows this, and even longer 
alternating series have been reported. The phenomenon may 
be strengthened by winking the eyes vigorously. The first 
positive after-sensation is due to inertia of the retinal pro- 
cesses; the first negative and all succeeding after-sensations 
are due to fatigue. 

White and black act in very nearly the same way as colors 

^ It is often called an after-image; this name is misleading, as the impres- 
sion is really a sensory, not an ideational process. 



176 SIGHT 

in respect to positive and negative after-sensations. Where 
a bright field is observed containing several different colors 
and grays, all the colors and grays reverse, but not always 
simultaneously; the bright colors and white shift first, and the 
outlying portions of a bright area may reverse before the cen- 
tral portions. The after-sensations of the darker portions of 
such a field disappear before the brighter after-sensations. 

Contrast. — Complementary effects may be brought about 
under certain conditions without moving the eye. If we place 
on a mixer a disk containing a ring of black and white sur- 
rounded by a uniform color (e.g., blue), when the disk rotates 
the black and white ring is not seen as gray, but is tinged with 
the complementary (yellow) of the surrounding color, A 
similar effect is noticed in the Meyer pattern. This is a 
checker-board of small green and gray squares covered with 
thin tissue paper. When we observe the pattern through the 
tissue paper the colored squares appear green, but the gray 
squares have a salmon tinge. When the tissue is removed the 
salmon effect disappears, but it may still be faintly noticed 
around the edges of the gray squares if the eyes are not rigidly 
fixated. The appearance of the complementary effect with- 
out eye movement is called simultaneous contrast. The comple- 
mentary color which appears around the borders when the 
eyes wander is a negative after-sensation. It is called suc- 
cessive contrast. 

Peripheral Vision. — A greater number of hues are distin- 
guished near the center of the retina than farther out toward 
the periphery. Each hue gradually fades into an unsaturated 
tint as the color stimulus passes from center to periphery. At 
the periphery all the hues disappear and only distinctions of 
gray are observed unless the stimuli are very bright. 

The limits of the retinal field for each color may be explored 
by means of the perimeter. [Fig. 40.] If we explore the entire 
field, above and below, right and left, and in diagonal direc- 
tions, it is found that the shape of the color zones is irregular. 



PERIPHERAL VISION 



177 



They vary considerably for different hues. In most persons 
the field for green is far more limited than for other hues. 
[Fig. 41.] 

In the retina the number of cones decreases from the center, 
where there are only cones and no rods, to the periphery, where 
there are no cones at all. 
It has therefore been sup- 
posed by some writers that 
the cones are receptors for 
color stimuli, and the rods 
for gray (mixed) stimuli. 
The fact that the cones are 
larger and apparently more 
differentiated than the rods 
gives support to this view, 
but the conclusion is not 
universally accepted. Ac- 
cording to another view, 
the cones are receptors for 
' daylight ' vision, while the 
rods are receptors for ' twi- 
light ' vision, that is, for dim 
illumination of the field. The 
absence of color sensation 
at the periphery is one of 
several peculiar phenomena 
which make it difficult to 
formulate a satisfactory ex- 
planation of the visual pro- 
cess. 

Color Blindness. — A still 
more perplexing phenome- 
non is color blindness. Certain individuals, otherwise nor- 
mal, fail to distinguish color hues in the same way as the 
average human being. They are not merely unable to dis- 




PiG. 40. — Perimeter 



Observer's chin is placed on rounded chin-rest 
A, which is so adjusted that one eye is directly 
over semicircular top of rod B, other eye being 
closed. A small hole througlf the axis at C serves 
as fixation point. Color stimulus is moved 
along one circular arm, D, of the perimeter to- 
ward or away from center, on a carriage. The 
arms rotate, so that all portions of the visual 
field can be explored. On far side of plate E 
(which rotates with perimeter arms) is fastened 
a disk, ruled radially and circularly to represent 
'latitude' and 'longitude' from center of vision. 
Experimenter records the readings on this disk, 
which is hidden from observer by E. [From 
Judd, after Meyrowitz.] 



178 



SIGHT 



criminate _^ne differences of hue (red from orange-red, etc.); 
but they may be quite unable to distinguish between certain 




.9 ^iV^' 



Fig. 41. — Color Zones of Retina 

Limits at which four colors disappear in passing toward periphery, determined for radii 
30° apart. Right eye. 

hues which lie far apart in the spectrum, such as red and 
green. Color blindness is either total or partial. 

Total color blindness is inability to distinguish between any 
colors whatsoever. To a totally color-blind individual the 
world appears like a photograph — a collection of gray shades 
without coloring. This condition is called monochromatism. 

There are three fairly distinct types of partial color blind- 
ness, which are popularly called red, green, and blue blindness. 
The first two, which are the most common forms, are some- 



COLOR BLINDNESS 179 

times grouped together under the general name of red-green 
bhndness. A red-green bHnd individual may be unable to dis- 
tinguish between the colors of the flowers and leaves of a red 
geranium. He will confuse a red shawl with a green shawl if 
the two are of about the same degree of brightness. He will 
distinguish readily, however, between bright red and dark 
red, and between bright red and dark green. The difference 
between the two types of red-green blindness is observed when 
the subject is tested for all the spectral hues and the bright- 
ness of these colors is compared. Individuals of the red-blind 
type are not sensitive to the extreme reds of the spectrum, 
and the region of maximal brightness is displaced towards 
blue-green; hence, red looks black and green a light gray to 
them. Individuals of the green-blind type are sensitive to all 
the colors, but see reds and greens as yellow. To the red blind 
the spectrum appears dark in the red region, then yellow — 
gray — blue; to the green blind it appears as yellow — gray — 
blue. The former type is called protanopia, the latter 
deuteranopia, from the order in which the cases were first 
classified. 

A third type of partial color blindness occurs in a few in- 
stances, where the individual is unable to distinguish between 
blue and yellow; this is called blue blindness or tritanopia. 
The spectrum appears as red — gray — green, with the violet 
end dark. As this type is fairly common in certain diseased 
conditions of the eye, many writers are inclined to classify 
all such cases as pathological. 

In partial color blindness of any type the entire series of 
hues which the subject can distinguish may be produced by 
mixing two colors, instead of three as in the normal eye. Par- 
tial color blindness is therefore called dichromatism. Normal 
color vision, as we noticed, requires three distinct color 
components to produce all the hues, and is called trichro- 
matism. 

The brightness or shade- value of any color may be deter- 



180 SIGHT 

mined by comparing it with gray. If a disk of a certain red 
hue be placed on the color mixer and a smaller disk, part 
white, part black, be set on the same axis, the proportion of 
white and black may be varied till the gray disk appears of 
equal brightness with the surrounding color. The proportion 
of white to black thus determined is the measure of brightness 
value for the red which we are examining. This proportion 
is called the brightness equation of the color. The brightness 
equations for various hues in the normal eye are different 
from those of the protanopic or red-blind eye, but practically 
the same as those of the deuteranopic or green-blind eye. It 
is thus possible to distinguish the several types by tests in 
which colors of different brightness are compared, A bluish 
red and a bluish green which would appear equally bright to 
the normal eye, though differing in color, would appear to the 
deuteranope as grays of equal brightness; to the protanope 
they would appear as a very dark gray and a very light gray, 
respectively. 

Color blindness in one form or another is present in about 
four per cent of the human race. Partial color blindness is a 
heritable character and is in some way linked up with sexual 
characters. Thus if a color-blind man marries a color-normal 
woman their children have normal color vision, but the sons 
of their daughters are likely to be color blind. In other words 
the character is transmitted to the male grandchildren through 
the daughters, in whom it is latent. Color blindness is far 
more prevalent among men than among women. Apparently 
females are color blind only when color-blind males marry 
females in whom color blindness is latent. 

Theory of Visual Qualities. — Several attempts have been 
made to explain the complex relations and peculiarities ob- 
served in visual qualities. What is required is to discover a 
physiological process, or rather group of processes, of such 
nature that when they are stimulated the various phenomena 
will occur through their interworking. It has been difficult 



THEORY OF VISUAL QUALITIES 181 

to picture a set of processes which would account for all the 
observed facts, ^ 

The most satisfactory explanation so far suggested is the 
theory devised by Christine Ladd-Franklin. According to 
this view visual sensations originally comprised only shades 
of gray. It is assumed that there exists in the rods and cones 
a certain substance called the color molecule, which when 
stimulated gives rise to sensations of gray and white. In the 
course of evolution the color molecules in the cones become 
differentiated into two components, one part exciting a neural 
process which yields sensations of blue, the other yielding 
sensations of yellow. Later, the yellow component becomes 
differentiated again into two components, one of which excites 
a process yielding sensations of red, the other a process yield- 
ing green. 

Certain specific wave lengths affect each one of the compo- 
nents, giving the sensations of primal red, green, and blue. 
A certain other specific wave length stimulates the red and 
green components in such a way as to excite the process be- 
longing to the ' older ' yellow component; the resulting sensa- 
tion is primal yellow. All other wave lengths stimulate two of 
the components and give rise to an intermediate color. When 
mixed waves strike the cones the resulting sensation is gray 
(or white), which is the original visual process of the undif- 
ferentiated molecule. The color molecules in the rods are 
not differentiated, and hence they always yield gray. 

This genetic visual theory recognizes the existence of three 
fundamental colors, red, green, and blue, out of which all other 
effects arise by combination; it also recognizes the four primal 
colors, each of which is unlike the other three. The chief diffi- 
culty of the theory is to account for the sensation of black. 

Visual Intensity. — In sight the intensity of sensation ife 
closely bound up with the white-black quality changes, and 
many of the intensity phenomena have been examined in pre- 
* See Appendix, "The Visual Process," p. 441. 



182 



SIGHT 



ceding sections. The Purkinje phenomenon and twilight 
adaptation may be treated as intensity relations. Pure in- 
tensity relations may be investigated by measuring least per- 
ceptible differences of brightness in the gray series. This is 
determined by comparing a certain gray taken as standard 
with a graduated series of slightly lighter or darker grays. 

The least perceptible difference at the white end of the scale 
may be determined by means of a M assort disk, which presents 




Fig. 42. — Masson Disk 



a white surface with a single broken black line of uniform 
thickness. [Fig. 42.] When this disk is rotated the black and 
white mix, giving a series of concentric rings, which become 
fainter towards the circumference. The last distinguishable 
ring indicates the proportion of black which, mixed with 
white, gives a sensation just perceptibly darker than white. 
The least perceptible brightness at the dark extreme may 
be determined as follows: The observer is placed in a dark- 
room with blackened walls. On a black surface before him 



VISUAL INTENSITY 183 

a pencil is fixed upright. A light of standard brightness is 
moved slowly toward the pencil from a distance till the sub- 
ject just observes the shadow cast by the pencil. The sen- 
sation of faint light discriminated from the shadow, is called 
the least perceptible brightness. Certain visual processes occur 
in the retina, however, even when no stimulus is present; 
so that the experiment really measures the brightness of ob- 
jective stimulation which is least perceptibly different from 
the eye's ' own light.' According to S. P. Langley the energy 
of the light which produces the least perceptible visual sen- 
sation under most favorable conditions is 0.000,000,03 ergs. 

Collateral Reading: 

Parsons, J. H., Study of Colour Vision. 

Helmholtz, H. v., Physiologische Optik (2d. ed.). 

Greenwood, M., Physiology of the Special Senses, chs. 10-20. 

Titchener, E. B., Text-Book of Psychology, sec. 14-22. 

Schaefer, E. A., Text-book of Physiology, article 'Vision.' 

Ladd and Woodworth, Physiological Psychology, Part I, ch. 8; Part II, 

ch. 2. 
Luckiesh, M., Color and its Applications, chs. 4-7. 
Ridgway, R., Color Standards and Color Nomenclature. 
Abney, W. de W., Researches in Colour Vision, Part I, chs. 2, 3, 14 ff. 
Spindler, F. N., The Science of Sight, esp. chs. 2, 3. 
Rood, O. N., Students' Text-Book of Color, chs. 8, 9, 12-14. 
Breese, B. B., Psychology, ch. 8. 

Judd, C. H., Psychology, General Introduction (2d. ed.), pp. 74-100. 
Pillsbury, W. B., Fundamentals of Psychology, ch. 4. 
Piersol, G. A., Human Anatomy, pp. 1436-1483. 
Luciani, L., Human Physiology (trans.). Vol. IV, chs. 6, 7. 
Hering, E., Grundziige der Lehre vom Lichtsinne. 
Ladd-Franklin, C, On Theories of Light-Sensation, Mind, N. S., 1893, 

2, 473-489. 

Practical Exercises: 

Test and describe your after-sensations of color. 

Describe your experience of visual adaptation in going suddenly from a very 
light to a very dark room and vice versa. 

Cut strips of colored papers (R, Y, G, and B) 3 inches long, | inch wide; 
paste each on a white card. Stand card on table in good light; walk back- 
wards till color becomes indistinguishable. Repeat for each color. 
Report distance for each, and any other phenomena observed. (De- 
scribe experiment in full.) 



CHAPTER X 



THE SENSES (continued) 

2. Hearing (Audition) 

Structure of the Ear, — The receptor organ for hearing is 
the ear; but technically the ear includes much more than the 
peculiar-shaped shell which projects from the side of the head. 
The outer shell serves merely to gather the stimuli and direct 
them into the channel which leads to the inner ear. The re- 
ceptor proper is a complex structure within the skull. 



Incus 

Malleus 



Semicircular canala 
Vestibule 
Cochlea 




Fig. 43. — Cross-Section of Ear 

Vertical section of right ear through meatus and tube, viewed from front. Oval 
window lies behind the stapes; round window behind initial letter T of word 
'tensor* at base of cochlea. [From Lickley.] 

The auditory organ is divided into the outer ear, middle 
ear, and inner ear.^ [Fig. 43.] The outer ear consists of the 
shell (concha), together with the tube (external meatus) 
^ A model of the ear should be examined if possible. 



STRUCTURE OF THE EAR 



185 



which passes through an opening in the skull and terminates 
in a vibrating membrane called the ear-drum (membrana 
tympani, tympanum). 

The middle ear lies in the head beyond the ear-drum. It 
consists of a cavity bounded by the drum on one side and a 




M. Malleus. I. iDCus. B. Stapes, t.m. Tympanic membnnes. 

Fig. 44. — Diagram of Middle Ear 
Showing position of the three bones and two windows. [From Lickley.] 

bony wall on the other; in this wall are two apertures, called 
from their shape the oval window and round window. Each 
window is fitted with a vibrating membrane. The middle 
ear cavity extends inward and downward as a narrow tube 
{Eustachian tube), which opens into the back of the mouth. 
The distinctive features of the middle ear, besides the two win- 
dows, are a chain of three small bones called the hammer, 
anvil, and stirrup. [Fig. 44.] The hammer bone (malleus), 
shaped like a rude primitive hammer, is attached at the handle 
end to the center of the drum, and at the middle is grasped and 



186 HEARING 

held in place by a tendon. The head of the hammer fits into 
the anvil bone (incus). (Note that the hammer is operated 
by vibrations of the drum at the handle end — the middle 
is rigid.) The anvil attaches to the arch of the stirrup 
bone (stapes), whose two ends are attached to the membrane 
of the oval window. When the drum membrane vibrates 
to and fro, the vibration is transmitted through this chain 
of bones to the oval window and causes the membrane of the 
window to vibrate back and forth. 

The inner ear or labyrinth is a very complicated cavity, only 
part of which serves the auditory function. The dorsal por- 
tion contains the semicircular canals and their appendages, 
which act as receptor for the static sense. [See page 211.] 
The portion of the labyrinth concerned with hearing lies 
in front of this (ventrally), immediately inside the two 
windows. It consists of (1) a cavity called the vestibule, 
which is formed by two rounded protuberances called the 
utricle and saccule; (2) a spiral structure resembling the 
shell of a snail and called the cochlea. 

The inside of the cochlea forms a spiral chamber which is 
divided lengthwise by partitions into three separate tubes 
filled with liquid. The three tubes lie side by side and follow 
the spiral windings from the base of the cochlea to its apex. 
[Fig. 45.] (1) One of these tubes, called the scala vestibuli, 
leads from the oval window. When the window vibrates 
back and forth a series of waves are transmitted the length 
of the scala vestibuli. (2) The second tube, called the scala 
tympani, terminates below at the round window. At the 
apex of the cochlea the two scalse are connected. Thus the 
vibrations from the scala vestibuli pass into the scala tympani 
at the far end and travel downward through it, passing out 
in vibrations through the round window. (3) The third tube, 
somewhat smaller than the others, is called the cochlear duct. 
It is separated from the scala vestibuli by the membrane of 
Reissner, and from the scala tympani by the basilar mem- 



STRUCTURE OF THE EAR 



187 



I a 



A mpultae 




Fig. 45. — Labyrinth and Section through Cochlea 

A. Right ear; perspective in same general plane as Fig. 43. Semicircular canals at left, 
cochlea at right; between them the two windows. 

B. Longitudinal section of cochlea, showing spiral windings of the scala tympani and scala 
vestibuli. The cochlea duct (not shown) lies between two membranes, which form a continua- 
tion of the spiral lamina (Lam. spiral, ossea) just this side of the plane of section. [Both figures 
from Smith and Elder.] 



brane. In a small canal within the cochlear duct, and attach- 
ing to the basilar membrane, is a system of rods and hair cells 
called the organ of Corti. [Fig. 46.] They connect with fibers 
of the auditory nerve and are the specific receptors for audi- 



188 



HEARING 



tory stimuli. The hair cells and rods of Corti are attached 
at the ends in such a way that they vibrate when waves 
pass through the cochlea. They gradually increase in length 
from the base to the apex of the cochlea. One or another is 
affected according to the wave length of the vibration, just 
as a tuning fork of given length is set in vibration by one par- 
ticular sound and not by others. 



tiumira/ut teetoria 



Older hear cells 



limbtu 




rurvefibrei 



fS0'.i'\';il€-Si'y-'.'':n-°-'-- 

tspiixiU I 1 ctUsofDeiura 

outer rod 
basilar menbrane 



»S3SiZS£. 



Fig. 46. — Organ of Corti 



Section perpendicular to direction of windings of the scalse. Bods (or fibers) of Corti are 
designated 'inner rod,' 'outer rod.' The rods and hair cells become longer in successive sec- 
tions toward apex of cochlea. [From Lickley, after Retzius.] 



Auditory Stimuli. — The auditory stimuli consist of molec- 
ular vibrations called sound waves. Sound waves are pro- 
duced by vibrations of the molecules composing solid, liquid, 
or gaseous bodies and by to-and-fro vibrations of strings and 
membranes. 

For practical purposes we may divide the sources of sound 
waves into three classes: (1) Vibration of air molecules, gen- 
erated in organ pipes and other wind instruments. (2) Molec- 
ular vibration of solids, produced by striking a bell, steel 
bar, xylophone. (3) Mass vibration of flexible solids such as 
tuning forks, stringed instruments, and drums. A tuning 



AUDITORY STIMULI 189 

fork is attached at one end and vibrates freely at the other; a 
vioHn string is attached at both ends and vibrates freely in 
the middle; the membrane of a drum is attached all around 
the edges and vibrates at the center. The vibrations of 
solids, whether molecular or mass, are usually transmitted 
through the air and reach the ear as air vibrations. They 
may be transmitted through the skull to the ear-drum if a 
vibrating tuning fork is pressed to the head. 

Sound waves are longitudinal vibrations; that is, the par- 
ticles move to and fro in the same line as the propagation of 
the wave itself. In this they differ from light waves, where 
the individual particles move back and forth at right angles 
to the line of wave propagation. [See page 161.] Looking 
along the line of wave motion at any moment there is first a 
region of compression, gradually passing to a region of rare- 
faction of the particles, and so on. 

The speed of propagation of a sound wave is uniform for any 
given medium. The denser the medium the slower the speed 
of transmission. In air the sound waves, whatever their 
character, travel at the speed of 332.4 meters (about 1000 feet) 
per second. Sound waves, like light, vary in two respects, 
wave length (rate), and amplitude (intensity). 

The length or rate of a sound wave is not a matter of its 
speed (which is uniform) ; it depends upon the distance be- 
tween successive ' pulsations ' along a given path. We may 
measure either (1) the number of compressions which reach a 
given point each second; or (2) the distance from one point 
where the particles are at their maximum compression to the 
next point where the same condition (phase) exists at the same 
instant. These two measures vary inversely with each other. 
The greater the number of sound waves in a given time, the 
shorter are the individual waves ; if the length of each wave is 
increased, the number of waves is lessened. 

The sound waves form a continuous series extending from 
very long to very short; but not all of these waves stimulate 



190 HEARING 

hearing. The human ear does not respond to sound waves 
more frequent than about 30,000 per second/ nor to those 
less frequent than about 16 or 12 vibrations per second. Be- 
tween these limits every length and frequency of sound 
wave affects the normal human ear and gives rise to an au- 
ditory sensation. Not all of the infinite number of rates be- 
tween 12 and 30,000 are distinguished as different qualities. 
We cannot, for example, detect any difference between the 
sensation due to a wave of 12,000 and that due to a wave of 
12,010 vibrations per second. 

Physiology of Hearing. — The physiological processes con- 
cerned in hearing were partly described in our examination of 
the ear. When the sound wave reaches the shell of the ear it 
is caught and transmitted through the meatus and strikes the 
ear-drum. The drum is set in vibration according to the rate 
and intensity of vibration, and the chain of bones (hammer, 
anvil, and stirrup) vibrate to and fro, the stirrup causing the 
membrane in the oval window to vibrate. This in turn causes 
the liquid which fills the cochlea to vibrate at a certain rate 
and intensity, and this vibration is transmitted up the wind- 
ings of the scala vestibuli and down the scala tympani. Dur- 
ing its passage it affects some one of the hair cells or Corti rods 
in the cochlear duct, which connect with fibers of the eighth 
cranial nerve; the vibration of these cells serves as stimulus, 
starting a nerve impulse in one or more of the fibers, which is 
transmitted along the nerve to the auditory center in the 
brain. 

Were it not for the flexible membrane in the oval and round 
windows the liquid in the cochlea would not take up the vi- 
brations from the middle ear. The connection between the 
middle ear and the mouth by means of the Eustachian tube 
prevents permanent loss of hearing from very intense stimuli. 
A very intense sound wave drives the ear-drum back so far 
that it adheres to the further wall; in such cases byswallow- 
1 Wundt gives the upper limit as 37,000-40,000. 



PHYSIOLOGY OF HEARING 191 

ing we force air from the mouth through the Eustachian tube 
into the middle ear, which drives the drum back into its nor- 
mal position. The action of the stimulus upon the receptor 
is a mechanical (vibrating) effect — not a chemical process as 
in sight. 

In man there is no motor function specifically attached to 
hearing. In some vertebrates the outer ear is furnished with 
muscles which serve to move the shell to right or left, enabling 
the animal to focus upon a sound just as we focus the eye 
upon a bright light. A rudimentary muscle for moving the ear 
still persists in man, but it is seldom under voluntary control 
and in any case the movement does not assist in hearing. Our 
only means of focusing sound is by moving the whole head. 

Characters of Auditory Sensation: Qualities. — DiflEerences 
in rate of physical sound waves give rise to different qualities 
in auditory sensations. Just as in visual sensations, we find 
a series of auditory qualities due to various single vibration 
rates, and a separate quality due to mixed rates of vibration. 
The former are called tones, the latter noise. Sensations of 
noise are not so distinct from tones as the corresponding visual 
impressions. A series of noise qualities may be distinguished, 
but their character is that of the dominant tone. Noise dif- 
fers also from gray sensations in that it is characteristically 
unpleasant. 

Tones (Pitch). — The different rates of vibration of sound 
waves give rise to a series of tone qualities, called pitch. Low 
vibration rates (few waves per second) cause sensations known 
as deep tones; high vibration rates (many waves per second) 
give rise to shrill tones. ^ 

Some individuals are able to recognize any tone, and to com- 
pare its pitch with that of other tones heard some time before. 
They will report that the standard pitch of a piano in one 

^ They are sometimes called lotv and high tones respectively, but these 
terms are liable to be confused with soft and loud, which represent intensity 
differences. 



1^2 Searing 

house is slightly deeper than that of a piano in another house, 
or that a tune is sung ' in a higher key ' to-day than yesterday. 
This is called recognition of absolute pitch. This ability is not 
possessed by many. Ordinarily tones are not ' individualized ' 
as colors are. Most persons find difficulty in identifying any 
specific tone after a lapse of time; consequently the tones have 
not received popular names corresponding to red, blue, etc. 

The tone produced by stimuli of 256 vibrations per second is 
adopted in scientific works as the standard pitch. It is called 
c^ Other tones are defined by their relation to this standard.^ 

The tone corresponding to 512 vibrations is observed to be 
closely related to c^ It is called c^. Similarly, the tone cor- 
responding to 128 vibrations stands in the same relation to 
c^ as c^ to c^. It is called c. The general relation of two to 
one is called the octave relation; it is the relation between any 
tone and the tone produced by twice or half its number of 
vibrations. 

The hufnan ear is very acute at distinguishing relationships 
among tones. This ability is known as relative pitch, and the 
relation is called an interval. Intervals are measured by the 
ratio of vibration rates of the two tones which compose it. In 
modern music only a few different intervals are used. They 
are all based upon simple numerical ratios between the num- 
ber of vibrations of the two tones. The octave ratio is 1 : 2; 
fifth 2:3; major sixth 3:5; major third, 4:5, and so on to the 
minor second 15 : 16 — the least simple ratio in common use.^ 
These relations have been elaborated into a series of tones 
called the musical scale. [Fig. 47.] 

The musical intervals bear no relation to the least observ- 
able differences of pitch. While the smallest tone interval 
used is the semitone, whose ratio of vibration is 15 to 16, 

^ In tuning instruments for musical performances a dififerent standard 
is used, called concer/ p^fc^ ; in this c' = 264. 

2 The names sixth, third, etc., are based on the number of keys covered by 
the interval on the piano or other fixed instrument. 







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194 HEARING 

the threshold of difference between tone sensations in most 
cases is far less. At 256 vibrations, which is in the medium 
range of hearing, we can distinguish normally between tones 
of 256 and 256.5 vibrations per second, a difference of ^ vi- 
bration. In the region of very shrill tones the threshold of dif- 
ference is much higher; in other words, the discrimination is 
less fine. In very deep tones discrimination is also less fine 
relatively than in the medium range. The trained human ear 
can distinguish altogether about 11,000 differences of pitch. 

Overtones and Timbre. — When a single tone is sounded, 
it is usually accompanied by subsidiary vibrations of twice, 
three times, four times, etc., the number of vibrations. If we 
pluck a violin string it will vibrate not only as a whole, but 
also in half lengths, thirds, quarters, or fifths, etc., accord- 
ing to the place where we pluck it. These subsidiary tones 
fuse with the original tone (the fundamental) and are distin- 
guishable only after considerable practice. They are called 
overtones. A fundamental with its overtones constitutes a 
simple clang. 

In simple clangs the overtones often fuse so completely as to 
be indistinguishable; the clang appears as a simple sensation. 
But even though the overtones are not distinguished they 
alter the total effect. This is observed when the same tune is 
played first on the piano, then on a violin, a cornet, etc. Dif- 
ferent instruments are characterized by various sorts of over- 
tones, so that we distinguish not merely the tune, but the 
kind of instrument. The specific character of a clang due 
to its overtones is called its timbre. Each kind of instrument 
has its own peculiar timbre; the human voice has a great 
variety of overtones and each individual voice has a timbre 
of its own. 

Combination Tones and Compound Clangs. — When two 
tones are heard at the same time they combine in such a way 
that their identity is partly lost. This combination effect is 
an instance of fusion. In tonal fusion the tones do not merge 



COMBINATION TONES 195 

together completely; with practice either of the components 
can be discriminated from the total impression. Tonal fusion 
is a different kind of summation process from that which oc- 
curs in sight. When different colors stimulate neighboring 
parts of the retina the sensations are distinct and the only 
modification which occurs in the combination is the contrast 
effect; this variety of combination is colligation (ch. viii). 
Fusion and colligation are due to different ways in which the 
separate nerve impulses are summated in the centers.^ 

When two distinct tones are sounded together, it is possible 
after practice to distinguish along with them a third tone, called 
the difference tone. Difference tones arise from the interac- 
tion of two sound waves. Suppose we strike two tuning forks, 
one of 256, the other of 255 vibrations. Then once every 
second the two waves will reinforce each other and make a 
louder sound; and once every second the two forces will be 
working against each other — the one pushing the particles 
forward, the other pushing them backward — so that the 
result will be a softer tone. This loud-and-soft effect consti- 
tutes a beat, and the number of beats is equal to the difference 
between the vibration rates of the two tones. When a tuning 
fork of 256 and one of 266 vibrations are sounded together 
there will be ten beats a second, and so on. As the differ- 
ence between the two tones is gradually increased the beats 
increase in number and at length become so rapid as to 
be indistinguishable; they then pass over into a deep tone, 
which is the difference tone. The rate of a difference tone is 
always equal to the difference of rate between the two pri- 
mary tones. 

When two tones differing by more than 16 vibrations are 
sounded together we may hear three tones — two primary 
and one difference tone; when three tones are sounded we 

^ When two different color stimuli are applied to the same retinal spot at 
the same time (or nearly so), as in color-mixing, the summation occurs in the 
process of stimulation, not centrally. 



196 HEARING 

may hear six — the three primary and the difference tone 
of each pair; and so on. The primary tones and difference 
tones fuse together into one complex impression. These 
complex sensations are called compound clangs. 

A noise may be regarded as the limiting case of a compound 
clang. It is composed of a very great number of tonal constit- 
uents. If we take into account all the observably different 
simple and compound clangs, the total number of auditory 
qualities is many times greater than 11,000. 

Intensity. — Differences in the amplitude (force) of sound 
waves produce intensity differences in the auditory sensation. 
To determine the least perceptible difference in auditory in- 
tensity a steel ball is dropped from a standard height and 
then from a slightly greater height. The variable height is 
altered gradually until the subject just notes a difference in 
intensity between the two sounds. 

The faintest audible sound is reported to be that produced 
by dropping a cork weighing 1 mg. from a height of 1 mm., 
the ear being 91 mm. distant. The upper limit of intensity 
has not been determined. Loud sounds tend to become more 
and more painful, and in the end produce actual injury to the 
ear-drum. 

3. Smell (Olfaction) 

Structure of the Olfactory Receptor. — The receptor for 
smell is far simpler than either the ear or the eye. In fact 
none of the other sense receptors begin to compare in complex- 
ity with the organs for sight and hearing, with the single ex- 
ception of the static receptor. 

The olfactory sense is closely associated with the function 
of breathing. Its receptor consists of a number of spindle- 
shaped cells situated in the mucous lining of the nostrils. 
[Figs. 48, 49.] Each olfactory cell is connected with a fiber 
of the olfactory nerve. In man the olfactory spindles are lo- 
cated in a small region far back within the nasal cavity at the 




Fig. 48. — Nasal Cavity and Olfactory Region 

Vertical section, viewed from front, passing through back of eyeballs. The olfactory 
region lies mainly at the upper end of the long, narrow passages at each side of the central 
dividing membrane (septum). [From Wenzel.l 




Fig. 49. — Olfactory Cells 

Section of olfactory mucous membrane, showing olfactory cells (OC) and nerve fibers (N) 
which connect with them. SC = supporting cell. [Based on Piersol.) 



1 



i 



STRUCTURE OF OLFACTORY RECEPTOR 197 

top of the passage way. In many animals, such as the dog 
and moose, this sense and its receptor are much more highly 
developed than in man. 

Olfactory Stimuli and Physiology of Smell. — The stimulus 
for smell consists of very minute particles which emanate 
from various objects (especially organisms) and permeate the 
surrounding air. They sometimes travel great distances. 
These emanations are drawn into the nostrils in breathing. 
As they pass through, some strike the olfactory cells and 
stimulate them. The process of stimulation is apparently 
a chemical action. The fibers of the first cranial nerve termi- 
nate at the spindles and carry the impulses to the olfactory 
center in the brain. The stimuli include many varieties, 
which produce different modes of impulse in the olfactory 
nerve. 

Sense Characters : Qualities. — Despite the apparent sim- 
plicity of the receptor for smell we distinguish many different 
qualities in the olfactory sensations. The olfactory qualities 
are called odors. So far as can be determined the odors do not 
form a continuous series like the color hues and auditory tones. 
Possibly further observation and experiment will bring them 
into serial order. The catalogue of qualities is by no means 
completed. New varieties of odor are often discovered when 

Table X. — Classes of Odobs 
Class Examples 

1. Ethereal All fruit odors 

2. Aromatic Camphor and spicy smells; anise, lavender, etc. 

3. Fragrant Flower odors; vanilla; gum benzoin, etc. 

4. Ambrosiac Amber; musk 

5. Alliaceous Garlic, asafoetida; bromine, chlorine, etc. 

6. Empyreumatic Toast, tobacco smoke; naphtha, etc. 

7. Hircine Cheese, sweat, etc. 

8. Virulent Opium, cimicine, etc. 

9. Nauseous Decaying animal matter, faeces, etc. 

[From Titchener, Exp. Psychol, Vol. I, Part II, p. 112; after 
Zwaardemaker . ] 



198 



SMELL 



we scent new fruits or flowers or new chemical compounds. 
At present all we can do is to group the olfactory qualities 
into a number of classes. The members of a class resemble 
one another in a general way and differ noticeably from those 
of other classes. Nine distinct classes are observed, each of 
which includes a large number of different odors. [Table X.] 
The so-called pungent odor is not an olfactory quality but a 
tactile sensation akin to tickling. 

Intensity. — Intensity differences in smell depend not so 
much upon the force of the individual stimuli as upon the 
number of particles which affect the receptor simultaneously; 
this varies with the density of the emanation. The least 
perceptible difference of intensity may be determined by 

means of a series of bottles 
containing the odorous sub- 
stance in different degrees 
of dilution. The more con- 
centrated the solution, the 
more particles will emanate 
from it, and hence the 
greater the intensity. 

Intensity tests are also 
made with the olfactometer. 
[Fig. 50.] This apparatus 
consists of two parallel tubes, 
curved at one end for inser- 
tion in the nostrils. Tubes 
lined with substances con- 
taining odorous particles 
are drawn over the straight end of the olfactometer; the in- 
tensity of the odor varies with the amount of exposed surface 
of odor-bearing substance. 

Either of these apparatus may be used to determine the 
threshold of intensity. The least perceptible intensity varies 
widely according to the substance used; for mercaptan it is 



^ 



^^ 



Fig. 50. — Olfactometer 

The two bent tubes at right are inserted in 
the nostrils. Solid frame conceals other end of 
tubes from the observer. Hollow tubes lined 
with odorous substance are shown at left, drawn 
partly over the olfactometer tubes. [From 
Titchener, after Stoeltlng.] 




Fig. 51. — Tongue, showing Papilla 

Taste bulbs are located in the circumvallate (C) and fungiform (Fu) papillee. None are 
found in the filiform (Fi) or foliate (Fo). [From Wenzel.l 



INTENSITY 



199 



about 0.000,000,043 mg. in a liter of air; this is one of the 
lowest thresholds. 

In man, smell is decidedly inferior in importance to sight 
and hearing, and even to touch and the muscle sense. It serves 
practically to warn us of danger from noxious substances; it 
has also developed a certain esthetic value comparable to that 
of music. On the whole this sense appears to be losing in im- 
portance with the progress of the human race; its data play a 
minor role in the mental life of civilized man. 



4. Taste (Gustation) 

Gustatory Receptor and Stimuli. — The sense of taste is 
closely related to smell. Their evolutionary history goes 
back to a common origin, the chemical or food sense. But 
whereas objects which arouse the smell sensation are often at 
a considerable distance from the body, the substances which 
we taste act only through contact with our organism. 

The receptors for taste are certain cells shaped like bulbs or 
flasks which are inserted in the mucous lining of the tongue 
and palate. [Figs. 
51,52.] These bulbs 
have a small open- 
ing at the ' neck ' 
end which receives 
the stimulus. The 
stimuli are always 
in liquid form; solid 
substances are tast- 
ed only when dis- 
solved by action of 
the saliva. Fibers 
from three distinct 
cranial nerves connect with the taste bulbs at various parts 
of the tongue and convey the impulses furnished by the 
stimuli to a taste center in the brain. 




Fig. 52. — Taste Bulbs and Taste Cells 

Section of lining of papillae, showing taste bulbs (TB), with 
pore (P) at neck and taste cells (TC) forming part of bulb; 
EC = epithelial cells. [Based on Piersol.j 



200 TASTE 

Characters of Gustatory Sensation. — Taste sensations are 
often mistaken for odors, and this confusion has led to the 
prevalent belief that taste affords a great variety of different 
qualities. Much of the food taken into the mouth consists 
of odorous substances. The emanations pass up into the 
nostrils and affect the olfactory receptor. From the location 
of the stimulating body the sensation is ascribed to taste. 
An onion and a potato differ decidedly in smell but not in 
taste. Unless a crucial test is made by holding the nose while 
eating, we invariably attribute part of their quality differences 
to taste. The combination of smell and taste makes up the 
flavor of food. 

Careful experimenters discriminate only four qualities in 
taste: 

Sweet 

Sour (or acid) 

Saline 

Bitter 

Some observers notice two other qualities, metallic and 
alkaline. These are probably due to a combination of taste 
qualities. Other so-called qualities of taste are fusions of 
taste sensations with sensations of warmth or cold and con- 
tact. The four qualities do not form a series ; they bear no 
special relation to one another except that sweetness contrasts 
to a certain extent with the other three. 

The least perceptible difference in intensity of tastes may 
be tested very much as in smell. Bottles are prepared with 
solutions of some tastable substance in varying degrees of con- 
centration. These solutions are applied successively to the 
tongue by means of a brush. Exact determination of the 
threshold is difficult, owing to the persistence of gustatory 
stimuli ; it is not easy to remove the tasteful substance from 
the tongue quickly enough to admit close comparison with 
the next stimulus. The least perceptible intensity of taste 
differs widely for the four qualities. [Table XI.] 



A 



CHARACTERS OF GUSTATORY SENSATION 201 



Table XI. — Thkeshold of Inten- 
sity FOR Taste 



Quality 

Bitter 

Saline 

Sour 

Sweet 



Dilution in water 



Substance 
Quinine 
Salt 

Sulphiu-ic acid 
Sugar 

[From Sanford, Exp. Psychol, p. 48, 
after Bailey and Nichols.] 



390,000 

2,240 

2,080 

199 



5-7. Cutaneous Senses: Touch, 
Warmth, Cold 

Receptors for Cutaneous Sensi- 
bility. — The outer surface of the 
body is susceptible to several kinds 
of stimulation. The resulting sen- 
sations are grouped together in 
popular language under the name 
of ' touch.' Careful investigation, 
both by self-observation and study 
of the cutaneous receptors, has 
led to the distinction between the 
sense of touch proper and senses of 
warmth, cold, and pain.^ The sen- 
sations of warmth and cold consti- 
tute distinct qualities, and their 
receptors appear to differ from 
each other and from the touch re- 
ceptors. 

A difference in quality is observed 
in touch between the sensations of 
contact and pressure. Some points 
on the skin are susceptible to 
warmth and not to cold; for other 
points the opposite is true. By 
^ For discussion of pain see p. 207. 




Fig. 53. — Pressure and 
Temperature Spots 

Map of palm of left hand, showing 
relative distribution of sensitivity 
to pressure (A), warmth (B), and 
cold (C). Same area represented in 
all, three cases. In A the regions 
marked black are relatively insensi~ 
live to pressure. In B and C the areas 
most sensitive (to warmth and cold 
respectively) are marked in black, 
less sensitive in lighter shading, etc. 
[From Schaefer, after Goldscheider.l 



202 



CUTANEOUS SENSES 



minutely exploring a section of the skin first with a warm 
needle and later with a cold needle, a map of the warmth 
spots and cold spots may be made and it is found that their 
locations in the given area are quite different. Pressure spots 
are mapped out in the same way and their topography differs 
from the other two. [Fig. 5S.] These spots may remain prac- 
tically unchanged for months. 







D E 

Fig. 54. — Types of Cutaneous Receptors 

A. Vater-Pacini corpuscle; longitudinal section from skin of child's finger. 

B. Transverse section of same. 

C. Meissner corpuscle. 

D. Free nerve endings in epidermis of rabbit. 

E. Merkel cells in interpapillary epithelium. 

F. Krause ond-bulbs from human conjunctiva. 

N = nerve fibers, [Based on several drawings.] 

Examination of the structure of the skin reveals several dif- 
ferent kinds of corpuscles embedded within it and apparently 
connected with nerve endings. The most noticeable of these 



CUTANEOUS RECEPTORS 203 

in man are the corpuscles of Vater-Pacini, Meissner, Krause, 
and Merkel. [Fig. 54.] Some of these types lie near the 
surface; others lie deeper in the skin. It is now generally as- 
sumed that these several types are receptors for different 
cutaneous senses. Observers are not in agreement as to which 
serves for which. 

The receptors for warmth apparently lie deeper than those 
for cold, since their response requires a longer time. There 
appear to be two different receptors for touch — one lying 
deeper than the other. In certain pathological conditions one 
kind of cutaneous sensation may be lost while others remain. 
These anatomical and pathological observations have led re- 
cently to a distinction between epicritic (surface) and proto- 
fathic (deeper-seated) senses. Cold is epicritic and warmth 
protopathic; the contact sensation is epicritic and pressure 
protopathic. The distinction as applied to warmth and cold 
is confirmed by self -observation, but it is not clear whether 
contact and pressure are distinct senses or merely two quali- 
ties of touch. 

The receptors for touch, warmth, and cold are distributed 
over the entire outer surface of the body. There are tac- 
tile corpuscles at the roots of the wide-spread body-hair; 
they are found also in the eyeball, tongue, and other spe- 
cial organs. Some of the inner organs are sensitive to contact 
and pressure but not to temperature stimuli. 

Qualities and Intensity of Cutaneous Sensations. — Each 
of the two temperature senses has one characteristic quality 
— warmth and cold, respectively. When the warmth and 
cold receptors are stimulated together the result is a sensation 
of complex quality known as the heat sensation. 

The sense of touch (assuming it to be one sense) has only 
two elementary qualities, contact and pressure; but under 
special conditions of stimulation it gives rise to certain pecu- 
liar quality effects. We distinguish in a qualitative way 
between sensations of roughness, smoothness, moving contact, 



204 CUTANEOUS SENSES 

moisture, and stickiness. The sensations of tingling and itch- 
ing appear to be touch quahties ; they are generated by stimuli 
within the body and are sometimes attributed to the organic 
senses. The pecuHar sensation known as tickle differs strik- 
ingly from most sensations in that a very faint stimulus yields 
a very intense sensation. The tickle sensation is probably 
due to a definite touch stimulus applied to a very small area. 
The other special touch qualities are due to spatial and tem- 
poral variations of the stimulus. 

Differences of intensity may be examined in touch, warmth, 
and cold by methods analogous to those used in the higher 
senses. The least perceptible intensity in touch is stated 
to be the contact of a cork weight of 2 mg. on the tip of the 
finger. For the temperature senses the least perceptible sen- 
sation is produced by a stimulus about | ° warmer or colder 
than the normal temperature. 

While the cutaneous sensations present no great variety of 
quality, they furnish considerable information about the 
near-by environment and indicate the mutual relations of 
different parts of the body. The data derived from touch are 
highly important in perception, especially in the determina- 
tion of space relations (ch. xii). Warmth and cold are less 
significant factors in mental life. Their data usually combine 
with tactile sensations to form complex experiences; they 
rarely yield separate perceptions, 

8. Organic Senses (Ccenesthesia, Visceral Senses) 

Classes of Systemic Sensations. — The senses so far con- 
sidered are affected by external stimuli. We come now to a 
group of senses which furnish data concerning the vital life 
of the organism itself. The whole group are called systemic 
senses. They include (1) senses associated with specific phy- 
siological processes; (2) general sensibility; and (3) the pain 
sense. The first two may be grouped together under the gen- 



CLASSES OF SYSTEMIC SENSATIONS 205 

eral name of organic senses; they are also called visceral senses 
and coenesthesia.^ 

Owing to the deep-seated location of their receptors the 
organic senses are extremely difficult to investigate, and our 
knowledge of them is still somewhat confused. Not only is it 
difficult to determine exactly the number of different sense- 
qualities, but it is uncertain how many of them constitute 
separate senses with distinct receptor organs. 

Qualities of Organic Sensations. — The most distinctive 
organic sensations are those associated with the digestive, 
vascular, and sexual functions. Among the digestive sensa- 
tions casual observation distinguishes between hunger and 
thirst. Under careful examination the sensation of hunger 
proves to be a complex phenomenon. It includes (1) hunger 
'pangs, due to muscular contraction in the stomach; (2) appe- 
tite or craving for food, which sometimes occurs even when 
the stomach is filled; (3) general discomfort due to starva- 
tion and depletion of the tissues. In addition to these we 
find (4) a separate sensation quality, which accompanies the 
satisfaction of hunger. Thirst is probably due to a drying of 
the mucous membrane in the pharynx. It is doubtful whether 
the sensation of satisfied thirst is distinct from general sensi- 
bility. Another digestive sensation is nausea, which possesses 
a very pronounced quality. There is also a specific sensation 
in the digestive tracts due to distension of the stomach and 
other cavities. Less definite sensations accompany the later 
digestive processes in the intestines, bladder, etc. There are 
also specific sensations connected with urination and defeca- 
tion. Associated with these is a sensation localized in the 
abdominal region, which is stimulated under emotional con- 
ditions of fright, anger, affection, etc. Although the above- 
mentioned sensation qualities are all associated with the di- 

^ The term organic sense is often used more broadly, to include muscle sen- 
sations; these belong to a dififerent class. Sensations from receptors in the 
thorax as well as in the visceral organs come under the head of organic senses. 



206 ORGANIC SENSES 

gestive processes they are due to distinct stimuli and in many 
cases probably involve distinct receptors. 

The circulatory processes are accompanied at times by dis- 
tinctive sensations such as flushing, heart quavers, and the 
like. The respiratory processes under certain conditions also 
give rise to distinct sensations. Sensations from both circu- 
lation and respiration appear in states of trepidation, anxiety, 
and panic. In general, however, these autonomic processes 
proceed without any distinctive sensations apart from a con- 
dition of general sensibility or feeling. 

The sexual functions give rise to distinctiye sense qualities 
known as sexual craving, orgasmic sensation, and sexual satis- 
faction. They probably contribute also to the tone of general 
sensibility. 

General sensibility or feeling is the obscure sensation which 
pervades the body at any given moment. It includes two op- 
posite qualities, pleasantness and unpleasantness. It is prob- 
able that general sensibility has no specific receptor of its own, 
but is due to certain common characteristics of the stimuli 
which affect the various organic receptors. The metabolic 
changes which occur within the body are of two opposite sorts : 
anabolism or building up of chemical compounds, and katab- 
olism or breaking down of existing compounds. Anabolism 
and katabolism probably stimulate all the receptor organs. 
They modify the impulses due to the specific stimuli for each 
receptor, and give rise to the two phases of sensation known 
as pleasantness and unpleasantness respectively. In the ex- 
ternal senses the specific characters of the stimuli are so 
pronounced that the general sensibility factor is usually of 
minor importance. In the organic senses (and pain) on the 
other hand, the specific mode of the stimulus is but little 
differentiated, while the metabolic stimuli are very pro- 
nounced. Hence the distinctive feature of organic sensa- 
tions in most cases is the feeling tone or general sensibility. 
An organic sensation is determined primarily by the meta- 



QUALITIES OF ORGANIC SENSATIONS 207 

bolic stimulus, and only secondarily by a specific type of stim- 
ulus. Most of our digestive and other organic sensations are 
observed chiefly as feelings of pleasantness or feelings of un- 
pleasantness; their specific sense qualities are subordinate. 

In addition to the general sensibility connected with specific 
organs, we experience a total feeling of sensibility in the body 
as a whole. This sensation is determined by the balance be- 
tween the various anabolic and katabolic processes which are 
taking place at the time; but it takes on a quality tinge of its 
own, due to the summation of various obscure sense-qualities. 
The total general sensibility is characterized, according to 
varying conditions, as well-being, repletion, drowsiness, dis- 
comfort, fatigue, vigor, weakness, and the like. 

9. Pain Sense 

Pain Stimuli and Qualities of Sensation. — The pain 
sense is distinct from the organic senses and general sensibil- 
ity, but like them it furnishes data concerning the vital life 
of the organism. No specific receptor for pain has been dis- 
covered. The stimulus apparently affects directly the free 
endings of a group of sensory neurons which terminate in 
various parts of the body, especially near the periphery. 
[Cf. Fig. 54 D.] 

Pain sensations occur in connection with sensations of other 
types. When a very intense stimulus of any sort is applied 
to the skin the specific receptor for warmth, cold, or pressure 
takes up only part of the energy. The remainder is diffused 
through the tissues and stimulates the free endings of the pain 
nerves. These nerves lead to a separate center in the brain. 
The pain sensation begins somewhat later than the specific 
sensation which accompanies it. 

Pain has a very prominent metabolic component, always 
katabolic. The sensation is characteristically unpleasant. 
Its specific qualities are difficult to discriminate from those 
of the accompanying sensations. Pain in the eyeball appears 



208 PAIN SENSE 

to have a different quality from the pain of a bruise or soreness 
of the skin. More probably the difference is not in the pain 
sensation itself, but is due to the blending of muscle or touch 
sensations with pain. We discriminate sharp, incisive pains 
from vague, diffused pains; but this distinction may be due 
to the number of nerve endings affected or to intensity of 
stimulation. The distinction between throbbing pains and 
prolonged pains of even intensity depends upon temporal 
variations of the stimuli. There is a marked difference, as 
Titchener points out, between the bright pains which origi- 
nate near the surface of the body, and the dull pains con- 
nected with the internal organs, but whether this constitutes 
a qualitative distinction is by no means certain. 

Pains are distinguished and named with reference to the 
accompanying sensations or according to their extent and 
duration. We distinguish between scratches, pricks, stings, 
and sores (touch); burns (temperature); stomach pains, 
nausea, intestinal pains (organic) ; bruises and muscular sore- 
ness (kinesthetic). Eye pains and earaches are organic; they 
are not connected with the special senses mediated by these 
receptors. ^ Headache is due to local stimuli in that region. 
Shooting neuralgic pains are apparently due to internal 
stimuli which affect the nerves at some point of their course. 
Toothache is due to stimulation of specific nerves which ter- 
minate in the teeth. 

However disagreeable the pain sensations may be in 
themselves, they play a prominent role in the life history of 
the individual, since they warn him of danger from without 
and within, and enable him to remedy harmful conditions. 
The elaborate mechanism for pain reception which has 
evolved among the higher organisms, and the prevalence 
of pain phenomena in these species, indicate the extreme 
importance of this sense in mental life. 

1 Certain eye pains are tactile; others are due to strain of the eye mus* 
cles (kinesthetic); occasionally they arise from intense visual stimuli. 



CLASSES OF MOTOR SENSATIONS 209 

10. Kinesthetic Senses (Muscle Sense) 

Classes of Motor Sensations. — We have examined two 
groups of senses : those which give information concerning ex- 
ternal objects, and those which report conditions within our 
own body. We now come to a third group — the senses which 
give information regarding our bodily movements and which 
indicate the position of our body in space and the mutual re- 
lation of its members. For want of a better term we may call 
this group the motor senses, although their data indicate posi- 
tion as well as movement. The motor senses include (1) the 
kinesthetic sense or senses, usually known as the muscle sense, 
and (2) the static or equilibrium sense. 

Kinesthetic Stimuli and Sensations. — Kinesthetic sensa- 
tions arise through stimulation of a group of sensory nerves 
which terminate in the muscles, tendons, and joints. The spe- 
cific receptors for these senses have not yet been identified, 
but the sensations themselves are readily observed. In cer- 
tain pathological conditions involving anesthesia of touch and 
temperature, the sensations attending movement of the limbs 
persist; conversely, in other diseased conditions, movements 
of the limbs yield no sensation while touch sensations persist. 
It has not been definitely determined whether the muscle, ten- 
don, and joint sensations constitute three separate senses, 
or are merely variations of a single kinesthetic sense. The 
term muscle sense is commonly applied to the whole group. 

Kinesthetic sensations are stimulated by movements of 
any of the striate (voluntary) muscles. [ See Fig. 20, p. 53.] 
The sensations may be observed by moving the finger, elbow, 
knee, eyelid, eyeball, tongue, neck, foot, etc. The impres- 
sion is quite different in quality from contact or pressure. 

The position of our members in space is also indicated by 
kinesthetic sensations. In most cases the muscles occur in 
pairs, one of which is antagonistic to the other. When a 
member is held rigidly in any position, each of the antago- 



210 KINESTHETIC SENSES 

nists is subject to a certain amount of contraction; the two 
resulting sensations together indicate the relative degree of 
muscular contraction and hence the position of the member. 
This may be observed if we close the eyes and hold the arm 
rigid in some position where it does not touch the body, or 
if we twist the neck to right or left and keep it fixed. 
When we flex the fingers or knee we obtain a distinct sen- 
sation of movement. 

The muscle-sense data are usually reinforced by tactile sen- 
sations, such as the scraping of the clothes against the skin, 
and by indications from other external senses. When the eyes 
are turned from side to side, the motion of the whole field of 
objects across the retina results in a general change of visual 
sensations; in walking we have a visual picture of the moving 
scene. These auxiliary motor indications from the external 
senses (touch, sight, hearing, etc.) are not properly speaking 
kinesthetic sen'sations at all, but they assist materially in our 
perception of position and movement; they may be termed 
secondary motor sensations. 

Kinesthetic Qualities and Intensity. — Careful observers 
report that the sensation obtained when the arm is moved 
differs in quality according as the movement is actively per- 
formed, or is made by someone else taking hold of the arm and 
bending it. Part of this difference, however, is due to contact 
and pressure sensations which accompany the forced move- 
ment. 

The quality differences among muscle sensations, joint 
sensations, and tendon sensations are few in number. When 
we are actively pushing, or lifting a heavy object, we obtain 
a sensation called effort; when a member is resisting external 
pressure there is a sensation of strain. These sensations are 
assigned to the tendons. When the muscles have been active 
for a long time a sensation arises of muscular fatigue; this is 
possibly a form of general sensibility. 

The intensity differences of the kinesthetic sensations are 



KINESTHETIC QUALITIES 211 

very pronounced and finely discriminated. A very slight 
movement of the finger or arm is readily observed, and the 
movements of our limbs are regulated very precisely by 
means of these indications. This may be easily tested by ob- 
serving how many different positions of the finger can be dis- 
criminated with the eyes closed. The least perceptible dif- 
ference of position for the middle finger is found to be 1°. 

The kinesthetic senses not only serve to inform us of our 
various postures and movements, but they also give informa- 
tion regarding the weight of external objects. If we lift a 
heavy object, the added resistance increases the intensity of 
the muscular contraction, and hence the intensity of the 
kinesthetic sensation is greater than when we merely raise 
the arm. 

Insofar as they furnish indication of the weight of objects 
the kinesthetic sensations might be classed among the ex- 
ternal senses. Their chief role, however, is the regulation 
of motor activity. 

11. Static Sense 

Static Receptor and Stimuli. — The receptor for the static 
sense is a complicated structure in the inner ear known as 
the semicircular canals. These canals are three in number 
and are placed at right angles to one another in three different 
planes, [Fig. 55.] They consist of osseous tubes filled with 
a liquid called endolymph. The semicircular canals connect 
with the vestibular portion of the inner ear at the utricle. 
[See Figs. 43, 45 A.] The latter (as well as the saccule) con- 
tain minute crystals called otoliths. The function of the utricle 
and saccule is not altogether clear. They may be sense organs 
which give data regarding position of the head in relation to 
gravity. 

The stimuli for sensations of the static sense are alterations 
in pressure of the endolymph which result from changes in 
the position of the head. Since the semicircular canals lie in the 



212 



STATIC SENSE 



three planes of space, any angular change whatsoever in the 
position of the head involves rotary motion of at least one 
canal about its axis. When this rotation occurs the inertia 

of the liquid inside the canal 
causes greater pressure at 
one end and less pressure at 
the other. Similarly, if the 
whole head is moved linearly 
in any direction the pressure 
at both ends of one of the 
canals will be increased or 
diminished. The changes in 
pressure of the endolymph is 
believed to stimulate nerve 
endings of one branch of the 
eighth cranial nerve; the re- 
sulting nerve impulses are 
carried to the static center 
in the brain. 

Since the canals are situ- 
ated in the inner ear and are 
supplied by a branch of the 
' auditory ' nerve, they were 
long supposed to have some 
function connected with hearing. It was found, however, that 
when the canals are excised in pigeons a very marked disturb- 
ance of motor coordination ensues. The bird is unable to 
regulate his flight or to maintain his balance. It is now well 
established that this organ represents a sense entirely distinct 
from hearing. Comparative morphology demonstrates that 
the sense of hearing arose much later in the animal scale than 
the static sense and is an off-shoot of the latter. In man, 
however, hearing has become so highly developed that it plays 
a far more important role in mental life. 

The static sense gives sensations of position and sensations 





.-••^ 


„«.?•« •tTjwr?»'*!»«^ 






1 




X 




m 




K 




m 


^^s^., ^_w 


r 




■-4i 








-§ 







Fig. 55. — Semicircular Canals 
[From Wenzel.] 



STATIC RECEPTOR AND STIMULI 213 

of motion. In both cases the static sensation is so closely 
bound up with muscle sensations and other kinesthetic data 
that it is difficult to distinguish its own particular quality. 
The sensation of motion apparently differs in quality from the 
sensation of position. The latter, as noted above, may arise 
in the utricle and saccule. The sensations from the three 
semicircular canals may also differ in quality; more probably 
the differences observed are similar in nature to the local 
signs found in the sense of touch, which enable us to distin- 
guish contact on the finger from contact on the arm, face, 
and elsewhere. 

The static sensations of motion vary in intensity according 
to the intensity of stimulation, which varies with the velocity 
of the movement. The differences of intensity may be ob- 
served by lying flat upon a rotation table, with eyes closed, 
while the table is turned at various rates of speed. The least 
perceptible motion is a rate of about 2° per second, starting 
from a standstill. 

The stimulus for static sensation is the acceleration of mo- 
tion, not the velocity. If we are rotated on the table at a uni- 
form rate, the sensation gradually dies away and we finally 
appear to be motionless.^ When this state of apparent rest 
is* reached, if the rate of rotation (hitherto uniform) be 
slowed up considerably, the subject obtains a sensation of 
motion in the opposite direction, though the table may still 
be rotating in the original direction. 

The data of the static sense combine with those of the 
kinesthetic senses and with motor data from the external 
senses to give information of our bodily postures and move- 
ments. All these data are intimately associated with the 
formation of motor habits and with the adjustments of move- 
ments generally. 

* The experience of rest is not perfect if the apparatus Jars or creaks. 



214 STATIC SENSE 

Collateral Reading: 

Ladd and Woodworth, Physiological Psychology, Part L ch. 8; Part II, 

ch. 1. 
Titchener, E. B., Text-Book of Psychology, sec. 23-59. 
Breese, B. B., Psychology, chs. 5-7. 

Judd, C. H., Psychology, General Introduction (2d ed.), pp. 101-126. 
Pillsbury, W. B., Fundamentals of Psychology, ch. 5. 
Dunlap, K., System of Psychology, ch. 4. 

Yerkes, R. M., Introduction to Psychology, Part II, chs. 11, 12. 
Luciani, L., Human Physiology (trans.). Vol. IV, chs. 1-5. 
Piersol, G. A., Human Anatomy, pp. 1391-1435, 1481-1523. 
Greenwood, M., Physiology of the Special Senses, chs. 1-9. 
Watt, H. J., Psychology of Sound, Introd. and ch. 1. 
Stumpf, C, Tonpsychologie. 
Zwaardemaker, H., Physiologic des Geruchs. 
Hollingworth and Poflenberger, The Sense of Taste. 
Crawford, J. F., in Psychol. Rev. 1898, 5, pp. 63-67, and references cited. 
Cannon, W. B., Bodily Changes in Pain, Hunger, Fear, and Rage. 
Moore, H. T., Pain and Pleasure. 
Warren, H. C, Sensations of Rotation, Psychol. Rev., 1895, 2, 273-276. 

Pbactical Exercises: 

Listen for difference tones and overtones on the piano (or violin, etc.) and 

describe the experience. 
Examine three dififerent sorts of organic sensations, e.g., hunger, general 

bodily fatigue, toothache. 
Observe the sensations of taste for various common foods while holding 

the nose, and compare with the usual sensations. 



CHAPTER XI 
THE COMPONENTS OF MENTAL STATES 

Mental States and their Components. — In earlier chapters ^ 
the distinction has been drawn between mental life as ob- 
served in others and our own mental life as each one of us 
observes it in himself. The latter is called subjective experi- 
ence. Consciousness is an abstract term which denotes the 
specific characteristic of these experiences — the fact that 
they form part of our own life. But there is nothing abstract 
about our conscious mental life. As we ' live along ' it con- 
sists of a series of definite concrete occurrences. 

Each separate conscious experience is called a mental state, 
and the same term may be applied more broadly to any part 
of an experience which is distinct enough to be discriminated 
out and examined by itself. Our present mental state is the 
sum-total of our conscious experience at the present moment. 
Usually we can analyze our present experience into a number 
of rather distinct partial experiences. We may at one and the 
same time perceive a landscape, feel a thrill of pleasure, recall 
an incident in the past, and plan some future action. Each 
of these may be regarded as a 'mental state.' 

Every one of our mental states in adult life is the result 
of a large number of nerve impulses, present and past, which 
combine together. Past impulses operate through their re- 
tained neural traces, and present simple impulses are sum- 
mated at the centers. Certain other operations take place in 
the act of combination.^ The result is a complex nerve im- 
pulse. It is these complex central impulses, observed by the 
individual himself, that constitute his mental states. The 

^ See chs. i and viii. 

^ See discussion of "Fundamental Operations of Nerve Substance," pp 
57-70, and of "Fundamental Operations of Experience," pp. 138-44. 



216 COMPONENTS OF MENTAL STATES 

simple impulses which enter into the complex impulses are 
called the components of mental states. 

The components of mental states are not observed sepa- 
rately, but we may study them in their simplest compositions. 
We cannot, for example, isolate a pure ' red sensation ' ; but 
we can examine a perception of ' red surface ' with the fewest 
possible complicating factors. To understand the nature of 
mental states we must first study the characteristics of their 
components. 

At the close of chapter viii a distinction was drawn be- 
tween two fundamental types of experience, sensory and idea- 
tional. Sensations are more fundamental data than ideas. 
Sensations are primary or original components of experience, 
while ideas are derivative components.^ 

1. Sensations 

Characters of Sensation, — In chapters ix and x we ex- 
amined the various classes of sensations separately. Under 
each sense we examined the mechanism by means of which 
the sensory neural process is stimulated and conducted to 
the centers, and noted the various qualities of sensations and 
their intensity differences. We shall now consider the char- 
acteristics common to all sorts of sensation, and the relations 
between the several senses. 

Sensations, we found, arise as a result of stimuli acting upon 
certain specialized cells called receptors, or in a few cases as 
a result of stimuli acting directly upon the free endings of 
sensory nerves. The differences among sensory nerve im- 
pulses and the variety among sensations depend (a) upon 
differences in the stimuli; and (b) upon the constitution of the 
receptor organs. In other words, to explain the dififerentiation 
of the sensory components of mental states we must look out- 
side the nervous system. 

^ Sensations and ideas may be grouped together under the name of im- 
pressions. 



CHARACTERS OF SENSATION 2l7* 

When a large number of sensations are observed and com- 
pared they are found to differ in two or more independent 
ways. Each independent manner of varying is called a 
character (or attribute) of sensation. The two most obvious 
characters of sensation are (1) Quality, and (2) Intensity. 
When the sensation is not limited to a single nerve impulse 
two additional characters may appear: (3) Duration, and 
(4) Extensity. 

R61e of the Stimulus. — The quality of a sensation depends 
ultimately upon the nature of the stimulus. Among sensa- 
tions arising through the same kind of receptor, quality differ- 
ences are due to the mode of stimulation. Thus differences 
among color sensations are caused by different rates of light 
vibration, and tone differences among auditory sensations 
are due to different rates of sound vibrations. Odor qualities 
are not caused by different rates of vibration, but are due to 
different ways in which various odorous particles act upon 
the olfactory spindles. The more striking differences be- 
tween quaHties from different receptors are also due to the 
modal factor. The visual sensation ' primal yellow ' is due 
to a certain rate of light wave, and the auditory sensation c^ 
to a certain rate of sound wave. These two stimuli differ in 
mode — the resulting sensations differ in quality. 

Intensity of sensation is quantitatively related to the inten- 
sity of the stimulus . As the intensity of the stimulus increases , 
the intensity of the sensation also tends to increase, though 
not in direct proportion. The relation is represented by the 
logarithmic curve, as Weber and others discovered (ch. v). 
It may be expressed by the following simple formula: "As the 
stimulus increases in geometrical proportion, the sensation in- 
creases in arithmetical proportion." ^ 

The two chief characters of sensation, quality and intensity, 
are, thus directly dependent upon certain corresponding differ- 

^ The experimental results in connection with Weber's Law axe treated 
in chapter xii. 



218 SENSATIONS 

ences in the stimuli which arouse these impressions. The 
duration of a sensation depends upon the duration of its stim- 
ulus,, but the relation is not so close. On the one hand the 
beginning of the sensation lags somewhat behind the appli- 
cation of the stimulus. On the other hand the sensation may 
persist after the stimulus ceases to act. In general, however, 
the longer a stimulus acts upon a receptor, the longer will be 
the duration of the ensuing sensation. Hence, the temporal 
character of sensation is primarily a function of the stimulus. 

Role of the Receptor. — The receptor is an essential factor 
in determining sensations. In the first place it is the receptor 
that determines whether or not any given force will act as 
a stimulus. There are many light waves of which we get no 
impression whatever, because the retinal elements are not 
capable of being stimulated by them. The infra-red and 
ultra-violet rays are just as much light waves as those within 
the limits of the visible spectrum; but their wave lengths 
are too great or too small, respectively, for the receptor organ. 
Thus the number of different qualities in each sense is limited 
by the capacity of the receptor. Moreover, there are forces 
in the environment for the reception of which no special organ 
has evolved. So far as we know, the magnetic force which 
acts upon the compass needle does not stimulate any receptor 
and gives rise to no sensation whatsoever. 

Again, the quality of each sensation is determined in part 
by the constitution of the receptor. The series of physical 
light waves is a straight progression, but the series of color 
qualities has four critical points, at red, yellow, green, and 
blue, and the two ends of the series approach toward each 
other in similarity. In the series of auditory qualities, too, 
octave tones resemble each other more than tones of any lesser 
interval. These special relations among sensation quali- 
ties are due to the structure of the receptors and the nature 
of their activity. 

The r61e of the receptor in determining the intensity of sen- 



ROLE OF THE RECEPTOR 219 

sation is not so important. In sight the intensity of the stim- 
ulus is modified by the receptor in several ways: (1) By con- 
traction or relaxation of the iris muscle the amount of light 
admitted to the retina is regulated. (2) The layers of the 
retina in front of the rods and cones absorb some of the rays 
and temper the stimulus. Very intense visual stimuli are 
also tempered by winking the eye. But while these are all 
part of the reception process, they affect the stimulus before 
it reaches the real receptor. 

The fact that the sensation intensity does not increase as 
rapidly as the stimulus intensity, indicates that it is affected 
either by the receptor or by the sensory neurons through 
which the impulse is transmitted. We do not know which. 
If Weber's Law held for all ranges of intensity the altera- 
tion might be accounted for by resistance and loss of nerve 
energy in transmission. But experiments show that the frac- 
tion of increase is greater for both very small and very great 
intensities than for medium intensities. This seems to indi- 
cate that the receptor is at least partly responsible for the 
loss in intensity. 

The duration of a sensation depends to some extent upon 
the receptor. The persistence of sensation after stimulation 
has ceased is due to a residual process in the receiving organ, 
and the lagging of sensation behind the stimulus is due in part 
to inertia of the receptor process. Negative after-sensations 
are due to metabolic activity of the receptors. 

One of the most important functions of the receptor is to 
furnish indications for the extensity (space) character of 
mental states. In those senses whose receptors are redupli- 
cated and receive similar stimuli at various points (rods and 
cones, touch corpuscles, etc.) each individual receptor element 
is slightly different from the rest. Every individual rod or 
corpuscle is affected in a slightly different manner, even when 
the stimuli are identical. Hence the sensory impulse, in ad- 
dition to its mode due to the stimulus, bears the mark of its 



220 SENSATIONS 

point of reception. These differences are called local signs 
(more properly, locality signs). 

The grouping together of local signs by the summation of 
impulses furnishes a new kind of variation to our experience. 
This fourth character of mental states is the extensity attri- 
bute. It varies independently of quality, intensity, and dura- 
tion. It is observed in mental states, not in their components. 
An object is perceived as large, extended, ' spaceful '; 
but the elementary sensations which compose it are not ex- 
tended or large. The extensity character of mental states is 
based, however, upon the different local signs of the sensa- 
tions which enter into their composition.^ 

Defective Receptors. — In certain individuals the normal 
condition of one or other of the receptors is altered through 
accident, disease, or specific inheritance. We noticed an 
instance of inherited abnormality in the phenomenon of color 
blindness. A corresponding defect, known as tone deafness, 
occurs frequently in hearing. The individual, while able to 
distinguish differences of pitch, is unable to recognize tone 
intervals, so that all tunes ' look alike ' to him. 

In such persons the range of one receptor or another is 
more limited than it is in the average man, either in respect 
to quality or intensity. As a result the individual experiences 
a lesser variety of sensations ; fewer different components enter 
into his mental states. The extreme case is where one sort 
of receptor is entirely destroyed or incapacitated. Blindness 
and deafness are well-known instances of this. Loss of smell 
(anosmia) and taste (ageusia) are not uncommon, but are 
less noticeable because these senses play a less important role 
in mental life. 

The effect of these abnormalities of the receptor upon the 
development of mental states is not so far-reaching as might 
be expected. Even the most extreme defects, such as blind- 

^ The manner in which space perception is derived from these sensory 
data will be treated in chapter xii. 



DEFECTIVE RECEPTORS 221 

ness and deafness, do not impair the normal course of mental 
life to the extent which we would suppose. If sensations of 
one class are lacking, data from other senses supply their 
place in large measure. The deaf learn to follow conversation 
by watching lip movements; the blind use touch and audi- 
tory data in finding their way about. There are two well- 
known instances in which sight and hearing have both been 
lacking, Laura Bridgman and Helen Keller, Both of these 
women by careful training attained a mental level above the 
average. 

These facts emphasize the extreme importance of the cen- 
tral system in organizing mental life, and the relative unimpor- 
tance of any one class of sensation. The receptors determine 
what material shall enter into our mental states, but the man- 
ner of composition is far more important than the nature of the 
components. 

Classes of Sensations. — The most obvious classification 
of sensations is according to their receptors. All the data 
received through the eyes are grouped together as visual sen- 
sations, and so on. This was the system used in the two pre- 
ceding chapters. 

A satisfactory classification of the senses is more difficult to 
arrive at. It depends largely upon what -we have in view. One 
scheme, often used in popular psychology, is based on the dis- 
tinction between special and common senses. The special 
senses have highly differentiated receptors and furnish many 
varieties of sensation. The common senses have simple re- 
ceptors, but these receptors are reduplicated many times and 
are scattered all over the body. Sight and hearing are the most 
specialized senses; touch and warmth are examples of com- 
mon senses. 

The senses are sometimes classed according to the process 
of stimulation. In sight, taste, and smell the stimulus pro- 
duces chemical activity in the receptor; in touch, hearing, and 
the static sense the stimulation is apparently mechanical. 



%%% SENSATIONS 

In comparative psychology the natural classification is 
based upon phylogenetic derivation. Hearing is an out- 
growth of the static sense, smell is an evolution from taste, or 
from the food-sense which preceded taste. 

A comparative study of the senses through the animal se- 
ries shows the greatest diversity in their evolution. Some 
appear early in history and advance rapidly (sight); others 
appear early but remain undifferentiated throughout the 
animal scale (touch) ; some appear late, and of these some de- 
velop meagerly (warmth), while others become highly differ- 
entiated (hearing). In a word, the senses exhibit the most 
bewildering irregularity in growth and differentiation. If 
we attempt to systematize them according to some Hegelian 
system of apriori logic we find it a hopeless task. 

This apparent absence of systematic development is read- 
ily understood if we realize that the origin of any receptor 
depends (1) upon the existence of a given force in the environ- 
ment, and (2) upon chance differentiation of certain cells so 
that they become capable of receiving this force. The per- 
sistence of any receptor and its degree of specialization de- 
pend also (3) upon its usefulness in the mental life of the 
creature. 

External, Systemic, and Motor Senses. — For our present 
purpose the most useful classification is according to the role 
which each sense plays in mental life. Some senses are es- 
pecially concerned in furnishing data from the environment 
outside the body. These are called external senses. Others 
report the condition of the internal organs and tissues. These 
are known as the systemic senses. A third group report oui- 
bodily movements and the position of the body or of its va- 
rious motile parts. These may be called the motor senses. 

The receptors fall into three fairly distinct groups following 
these lines. (1) Certain kinds of receptors lie at or near the 
suiface of the body and are excited by stimuli lying outside 
of the organism. They are called exteroceptors. (2) Other 



EXTERNAL, SYSTEMIC, AND MOTOR 223 

receptors lie in proximity to the internal organs concerned in 
digestion, circulation, breathing, sex functions, etc. Their 
stimulation is brought about by the physiological activity of 
these organs. They are called interoceptors. (3) The third 
class of receptors lie in proximity to the motor organs and are 
stimulated when the muscles contract.^ These receptors, al- 
though they lie within the body, bear a very different relation 
to mental life from the interoceptors. They give us an indica- 
tion of our own movements and assist in our motor control. 
These receptors are termed proprioceptors. 

The sensations furnished by these three groups of senses 
form the basis of very different types of mental states. The 
older psychologists recognized this in their distinction between 
cognitive, affective, and conative states or ' mental powers.' 
But in reality mental states are not so sharply demarcated as 
their components; the distinction applies to sensations rather 
than to full-fledged experiences. 

Number of Different Sensations. — We cannot at present 
make any satisfactory estimate of the number of different 
sensory data which enter into the mental life of the average 
human individual. In sight there are believed to be about 
30,000 distinguishable hues, shades, and tints; but if each rod 
and cone of the retina modifies its data by its own local sign, 
this would multiply the number by quite a large factor. ^ In 
hearing there are about 11,000 distinguishable tones; this num- 
ber must be multiplied by a large factor to include the differ- 
ent intensities. There are no local signs in hearing, but if we 
treat the ' clang ' as an elementary datum of experience the 
number must be multiplied still further to take in the many 
differences of timbre and the enormous variety of complex 
clangs which can be distinguished. 

^ The static sense belongs to this group, although its receptors are not 
connected with the motor organs. 

^ Not by the total number of rods and cones, however, since colors are not 
distinguished at the periphery. 



224 SENSATIONS 

There are many different qualities and intensities in smell, 
four qualities and many intensities in taste, with a few local 
differences. In the remaining senses the qualities are few 
in number but there are many distinguishable intensities. 
Local differences are numerous in touch and the kinesthetic 
senses, and somewhat less marked in the two temperature 
senses. 

Taking into account the variations of quality, intensity, and 
locality in every sense, it is apparent that we are capable of 
receiving a vast number of different sensations as data of 
experience. The total number is more probably over a million 
than under that figure. Since the local signs of the receptors 
alter the mode of the nerve impulse, it may be stated as a 
general law that all differences in sensory characters are due 
to variations in the mode or intensity of nerve impulses. 

Summary of Sensation. — Sensations are the original data 
which enter into the composition of mental states. The char- 
acters of sensation depend first of all upon the nature of the 
stimulus; but they are determined also to some extent by the 
constitution of the receptor. 

The stimulus is more important than the receptor in deter- 
mining the quality and intensity of sensation; but the differen- 
tiation of the receptor determines the number of discriminated 
qualities and intensities in any given sense. If a certain type 
of receptor is defective in any individual the range of the cor- 
responding group of sensations is narrowed; if the receptor 
is destroyed or cut off from the sensory neurons the corre- 
sponding sensations are lacking altogether. 

The stimulus determines the duration of a sensation, sub- 
ject to a certain factor of deviation due to the operation of the 
receptor. The extensity character of mental states — the 
size and shape of the experience — is not due to the stimulus, 
but to the local signs of the receptors. '^ 

^ Distance away from the body is partly determined by the stimulus; see 
chapter sii. 



SUMMARY OF SENSATION 



225 



The senses are divided into three classes : external, systemic, 
and motor, which perform different roles in mental life. The 
classification is shown in Table XII. 

Table XII. — • Classification of the Senses 



Class of Senses and 
Receptors 

1. External (exteroceptors) 

a. Distant 

(teleoceptors) 

b. Contiguous 

(proximoceptors) 

2. Systemic (interoceptors) 

3. Motor (proprioceptors) 



Senses 

( Sight 
< Hearing 
( Smell 
[Taste 
I Touch 
I Warmth ) 
I Cold f 
\ Organic 
) Pain 

( Kinesthetic 
) Static 



Sense Qualities 

Colors (hues, shades, tints), grays 

Tones, noises, timbre 

Odors of nine classes 

Tastes 

Contact, pressure, etc. 

Warmth, cold, heat 

Digestive, vascular, sex, etc. 
Pains of various organs 
Muscle, tendon, joint 
Position, progression, rotation 



2. Ideas 

The Ideation Process. — In this book the word idea ^ is used 
to denote any component of our mental states which is not 
the direct result of sensory stimulation. It should be borne 
in mind, then, that when we speak of ideas we do not mean 
full-fledged memories or any other image-states, but the ele- 
ments which go into the composition of such mental states. ^ 

An idea is an element of conscious experience whose quality 
does not correspond to the mode of any present stimulus 
or sensory impulse. Indirectly, every idea is the result 
of past sensory stimulation. For example, I hear the word 
' McCosh,' and immediately afterward the image of my first 
teacher of psychology is " present in consciousness." The 
sound of the word calls up the image by suggestion; but 
there is no similarity between the sound which I hear and my 

* The adjective is ideational, not ideal. 

' This meaning of the term idea has considerable historic support, though 
it differs from popular usage. 



226 IDEAS 

visual image. Or again, I see a cardboard box and an iron 
box side by side; one ' looks ' light to me, the other ' looks ' 
heavy. The lightness and the heaviness do not directly 
correspond to any present stimulus — they are kinesthetic 
states, while the stimuli are visual. 

In both these examples the mental states are made up in 
part of ideational elements. An idea is due to a nerve im- 
pulse in some part of the brain. But the quality of the idea 
does not correspond to the mode of the stimulus. The 
impulse has been modified and entirely made over. The re- 
sulting mode of the impulse (and quality of the impression) 
is determined by the retention effect of the neurons in some 
brain center. The set of the neurons has altered the mode 
of the nerve impulse as it passed into that region. Originally, 
this set was caused by sensory stimulation. 

The rise of an idea may be pictured as follows: A sensory 
stimulus sends a nerve impulse to the brain. At some syn- 
apse in its central course, part of the impulse is distributed 
from the main path into an adjacent neuron. This over- 
flow current, being less intense, loses its own mode and takes 
on the characteristic mode of the neuron into which it passes, 
this mode being determined by the trace left by past stimu- 
lation. The resulting central process is not a sensation, but 
an idea; it no longer retains the characteristic of its own 
origin. Not only may a sensory impulse be modified into an 
ideational impulse, but one ideational impulse may be mod- 
ified into another in the same way. In subjective terms, a 
sensation is transformed into a very different idea, or one 
idea is transformed into another. 

Ideation depends upon a complex, branching system of 
neurons in the brain; for if there is but one path of neural 
discharge there will be no overflow current and consequently 
no ideational experiences. Even in the species of animal 
just below man the mechanism for ideational processes is im- 
perfectly developed. In the transition from lower primates 



THE IDEATION PROCESS 227 

to man the development of the brain took a tremendous leap. 
In man there are many higher centers which receive im- 
pressions and retain traces. These centers are intercon- 
nected by association paths; a stimulus received at one 
center frequently passes to another, to still another, and so 
on indefinitely. This makes possible a long succession of 
ideational experiences before the nerve current passes over 
into motor paths. In a word, man has a mechanism which 
makes possible a highly intricate ideational life in addition 
to his sensory life. Among civilized races this type of 
experience has been especially developed and has come to be 
a most important factor in mental life. 

R61e of Ideas in Mental Life. — Ideational experiences 
bring about a more systematic and thoroiigh adjustment of 
our reactions to our total environment. They act in a variety 
of ways. 

(1) Ideas intervene between the sensory stimuli and our 
motor responses. At times a series of images or thoughts 
occur before the responsive activity begins. This delay 
serves as a check upon hasty and uncoordinated actions; it 
enables man to respond to the general situation, instead of to 
each particular stimulus. 

(2) The ideational factors in our experience extend the 
environment to include our past as well as our present life. 
They build up a continuing personality in the individual, 
and add a temporal dimension to his mental life. 

(3) Ideational experiences ' tone down ' the effect of present 
stimuli. They lend perspective to one's whole life and career. 
A being with a well-developed store of ideational experiences 
is less centered upon the here and the now than one who lives 
and acts mainly upon immediate sensory situations. 

(4) The growth of ideational life in man leads to a higher 
type of experience than imagery; the image develops into 
symbolic thought and reasoning, which form the basis of scien- 
tific knowledge and assist in a remarkable way to bring our 



228 IDEAS 

behavior and conduct into conformity with the objective 
world. 

Distinction between Ideas and Sensations. — We noticed 
that sensations are the original data of experience. Ideas 
are derivative. Their quality is determined by the trace left 
in one or more of the cerebral neurons by some earlier im- 
pulse or by a number of similar impulses. In respect to 
quality elementary ideas are similar to elementary sensations, 
and the same relation holds of composite ideas and composite 
sensations unless the retention trace has been modified by 
dissimilar impulses occurring meanwhile. This qualitative 
correspondence is noted by observers who have prominent 
imagery of one sort or another. A good ' visualizer ' can 
picture red, or he can picture the appearance of a friend's 
face. In either case the ideational experience is qualita- 
tively like the original sensory experience. The same is true 
when (for example) we image the sound of the Meditation 
from Thais as played by a violin. 

It follows, then, that we do not distinguish between ideas 
and sensations on the basis of quality. Ideas may be clas- 
sified into the same divisions as sensations — visual, auditory, 
etc., except that in most individuals many of the sense classes 
do not have corresponding ideas, so far as can be directly 
observed. 

Despite this correspondence, however, few of us have 
difficulty in distinguishing between sensory and ideational 
experiences, or between the sensory and ideational com- 
ponents in any given experience when we observe it carefully. 
The basis of this discrimination is two-fold: (1) the intensity 
of the data; and (2) in case of the external senses, the con- 
trollability of the data. 

(1) The intensity of an idea bears no relation whatever to 
the intensity of the original stimulus; it depends entirely 
upon the strength of the present nerve impulse. In most 
cases the overflow current which arouses an ideational ex- 



IDEAS AND SENSATIONS 229 

perience is comparatively weak. If we compare our memory 
or imagination of a sound with a sound sensation, we jBnd in 
most cases that the memory and imagination images are far 
less intense than the sensation. Our ' picture' of a face is 
a less intensive experience than our perception of the same 
face. Reduced intensity is the mark by which we most fre- 
quently identify an idea as such and distinguish it from 
sensation. 

(2) A second distinguishing mark between ideas and sen- 
sations is the independence of the latter. This criterion 
applies chiejfly to the external senses. External stimuli lie 
outside of our organism; they form part of the objective 
world. Ideas depend upon our own past experiences. In 
consequence, sensations from the external senses are more 
independent of our system of activity than ideas; every now 
and then they provide something wholly new and unex- 
pected. This independence is less noticeable in the systemic 
and motor senses. Kinesthetic sensations are generally pro- 
duced as a result of our own motor impulses, and many 
organic sensations are due directly or indirectly to our motor 
activity. Both classes are capable of being stimulated by 
neural activity; they are said to be ' under control.' Ex- 
ternal stimuli are not under direct neural control; hence, 
when we arouse a visual or other external experience we class 
it as ideational. 

Border-line Experiences. — These two criteria, intensity 
and independence, serve in most cases to distinguish sensory 
from ideational states. But they are not infallible tests. A 
sensory impulse may be so faint that the resulting impression 
is classed as an idea — or we may be uncertain as to its source. 
A similar confusion arises when an ideational nerve impulse 
is extraordinarily intense. 

Dreams have all the vividness of sensations, owing to the 
absence of actual sensory impulses with which to compare 
them. Some of our most annoying hallucinations are due to 



230 IDEAS 

ideas which are so vivid that we class them as sensations. In 
conditions of high-strung tension we see a specter before 
us, or hear voices warning us, though the mental state is 
really ideational. At times we question whether a sound 
which we hear is ' real ' — that is, whether it arose from ex- 
ternal stimulation or was the product of central excitation. 
On dark nights we are not certain what we actually see and 
what we only imagine. 

If the object appears to act independently of our control 
our error may be reinforced, or our uncertainty may be 
greater. In such cases the normal individual falls back upon 
a third criterion, the uniformity and general consistency of 
experience. We convince ourselves that the ' specter ' is 
imagined, that the ' voice ' is within us, because such experi- 
ences do not conform to the general scheme of things. Even 
in dreams the inconsistency of the experience occasionally 
convinces us that we are asleep. 

The criteria by which we distinguish ideas from sensa- 
tions are merely practical tests, based upon the general run 
of experience. In most cases there is a sharp dividing line, 
and the bulk of our experiences fall naturally into one class 
or the other. But neither the mental state nor its elements 
furnish a decisive indication of their original source. Both 
sensations and ideas are central processes; one sort may read- 
ily be mistaken for the other if its characteristics fall within 
the border-line territory. 

Classes of Mental States. — Mental states are classed 
according to the kind of elements which compose them. In 
point of fact our actual experiences are rarely if ever made 
up wholly of elements of one sort. A perception usually has 
some ideational tinge, and our motor experiences are rarely 
devoid of some ' feeling ' component. But in most of our 
mental states one or more types of element predominate; and 
for purposes of examination we classify the states which enter 
into mental life on the basis of their dominating components. 



CLASSES OF MENTAL STATES 231 

We distinguished between three kinds of sensation: ex- 
ternal, systemic, and motor. Each of these gives rise to a 
corresponding type of idea. But only ideas of the external 
type develop sufficiently to act as dominant element in 
mental states. Ideational processes of the systemic and 
motor types lead almost invariably to stimulation of a cor- 
responding sort and produce a sensation which supersedes 

Table XIII. — Classes of Mental States 

Primary 
Mental State Dominating Componeni 

Perceptions External Sensations 

Imagery External Ideas 

Feelings Systemic Sensations 

Conations (Expressive States) Motor Sensations 

Secondary 
Mental State Dominating Components 

Emotions Systemic and Motor Sensations 

Sentiments Ideas and Systemic Sensations 

Volitions Ideas and Motor Sensations 

Thought and Language (Social) Ideas and Motor Sensations 

Ideals and Rational Actions (Social) . Ideas; Systemic and Motor Sensations 

the idea. When we think of a doleful occurrence the 
glandular processes are stimulated and the resulting experi- 
ence is a sensation — a ' feeling ' of sadness rather than an 
idea. In the same way if we think of making a movement 
we almost invariably send an incipient motor impulse along 
the proper channel, so that the motor picture is supplanted 
by an actual kinesthetic sensation. 

A similar reinforcement occurs in the case of certain ideas 
derived from the external senses. When I think of a sound 
the muscles of my vocal chords are adjusted by a motor 
impulse and may bring about a whisper or incipient vocal- 
ization, so that the ideational processes are reinforced by 
a sensory stimulus. But in general the external senses are 
beyond motor control; the ideational experiences derived 
from them are not reinforced by corresponding sensations. 
A visual idea is not supplanted by a corresponding visual 



232 COMPONENTS OF MENTAL STATES 

sensation, and an olfactory idea does not bring about an odor 
sensation. We find accordingly that a class of mental states 
has developed whose chief components are * external ' 
ideational elements; but there are no well-developed mental 
states whose chief components are systemic or motor ideas. 

Mental states may be divided into primary and secondary. 
Primary states include those in which one single sort of com- 
ponent predominates ; secondary states are those in which two 
or more different types are prominent. There are four kinds 
of primary mental states: (1) Perceptions, in which the chief 
components are external sensations; (2) Feelings, based upon 
systemic sensations; (3) Conations or expressive states, based 
upon motor sensations; and (4) Imagery, based upon ideas 
derived from external sensations. Besides these, five well- 
developed secondary types are found in man.^ A list of the 
primary and secondary mental states with their chief com- 
ponents is given in Table XIII. 

Collateral Reading : 

James, W., Principles of Psychology, Vol. II, chs. 17, 18. 

Titchener, E. B., Textbook of Psychology, sees. 10-13, 112-114. 

Royce, J., Outline of Psychology, chs, 4-6. 

Stout, G. F., Manual of Psychology, Book IV, eh. i. 

Judd, C. H., Psychology, General Introduction, (2d. ed.), chs. 4, 5. 

Dunlap, K., System of Psychology, chs. 3, 6, 10. 

Ogden, R. M., Introduction to General Psychology, chs. 7, 8. 

Pillsbury, W. B., Fundamentals of Psychology, ch. 6. 

Breese, B. B., Psychology, ch. 4. . . 

Practical Exercises: 

Make a list of your experiences during 15 minutes (e.g., just after the 
close of the last lecture yesterday). Classify according to their notice- 
able components. 

Describe any experiences you can recall where you have mistaken an im- 
agination for a perception or vice versa, or where you were unable to 
judge its real nature. 

Analyze your total experience at some given instant (e.g., one minute be- 
fore you first thought of starting this problem), and pick out its vari- 
ous sorts of components. 

^ The primary states are treated in chapters xii and xiii. For conven- 
ience imagery is taken up immediately after perception. The secondary 
states are discus.'jed in chapters xiv and xv. 



CHAPTER XII 

PKIMARY MENTAL STATES 

1. Perceptions 

Nature of Perception. — Perceptions are mental states 
whose chief components are external sensations. The dis- 
tinctive feature of perception is that many nerve impulses 
coming in separately from external receptors are combined 
so as to constitute a single complex experience. When we 
look at a painting we do not see a great number of color 
patches, each independent of the others; we perceive the 
picture as a whole. The sensations may differ in locality 
and coloring, but they form part of a unit experience. The 
specific neural basis of perception is the summation process. 
The separate sensory impulses from various neurons are 
collected into a single neuron at a higher level in the brain. 
The corresponding subjective process is combination. 

In general our perceptual experiences correspond very 
closely to objects and events in the world outside' our body. 
The space and time relations of objects and object-groups 
are fairly well reproduced in our central neural states. This 
general correspondence between external objects and the 
experiences which they arouse suggests a number of specu- 
lative questions about our knowledge of the outer world, 
which need not be discussed here. ^ But certain facts should 
be noted: 

(1) The neural operation involved in perception takes 

place within the brain; it is a process of combining many 

nerve impulses which have reached the brain separately. 

This explains why our perceptions do not correspond in 

1 See Appendix, "Perception of the External World," p. 416. 



234 PERCEPTIONS 

every particular to the external objects which furnish the 
stimuli. 

(2) Certain objects and forces in the environment are not 
perceived at all. We do not perceive ultra-violet colors, nor 
do we perceive the magnetic earth-current except by some 
indirect means, such as watching a magnetic needle; neither 
do we perceive objects visually, however near they may be, 
if they lie behind a stone wall. In such cases there are no 
sense data for the perception process to work upon. 

(3) On the other hand, where sense data are present, the 
relations of objects and of their parts are perceived with 
greater exactness than the data warrant. When we look at 
a table we perceive the top as rectangular (as it actually is), 
even though the retinal picture has two acute and two obtuse 
angles; here the sensation group is diamond-shaped, yet we 
interpret the data correctly in perception, and perceive the 
object as a rectangle. 

Perception includes several different kinds of combination. 
Besides mere grouping of data, it furnishes us discrimination, 
superficial space relations, object groups, temporal relations, 
subordination of parts, solidity j and perspective. These 
phases of perception appear to have arisen successively, in the 
above order, in the course of animal evolution; in the human 
child there are indications of a similar serial growth. For 
convenience we shall examine them in a slightly different 
order : 

Simple perception 

Surface perception 

Depth perception and projection 

Apperception (focused perception) 

Object perception 

Perception of events, time, and rhythm 

Perception of difiFerences (discrimination) 

a. Simple Perception. — In most of the senses a number of 
stimuli occur together at the same time. When we open our 
eyes the whole visual field is usually stimulated at once. 



SIMPLE PERCEPTION 235 

In touch we are usually brought into contact not with a 
single point but with a region of stimulation. We usually 
hear not a single tone, but a complex sound or clang. In all 
these cases the stimuli are separate. Each rod and cone of 
the retina is provided with a separate neuron connecting with 
the visual center of sensation in the brain. Each corpuscle 
in the skin, each hair cell in the ear, is similarly connected 
with its own brain region by means of an individual nerve 
fiber. When the whole field of vision is stimulated the im- 
pulses from the individual rods and cones are carried sepa- 
rately to the brain. At each center (visual, tactile, auditory, 
etc.) these impulses are combined. As a result we ' see ' a 
mass of colored points, we ' palp ' a mass of touches at once. 
Our experience in any such case is not a single sensation, but 
a group of sensations which form a simple unit. The result- 
ing mental state is called a simple perception. 

In certain cases the impulses from two similar receptors 
unite to form a single impression. Thus in sight the impulses 
from the two centers of vision yield one impression, and so 
for each pair of ' corresponding points ' in the retina. We 
see the whole field of binocular vision as a single field, not 
in duplicate. This is called binocular fusion.^ In the same 
way a tone which stimulates both ears is heard as one tone, 
not two. 

Most of our perceptual states go beyond the stage of simple 
perception. We perceive two patches of color as larger and 
smaller, as lying one above the other, etc. This leads to a 
higher stage of perception, in which the mental state in- 
volves space relations. 

b. Surface Perception. — One of the most interesting 
problems in psychology is to explain how we perceive the 
size and shape of things and the relative position of different 
objects. The mental state which includes these relations is 

^ Where different colors are presented to the two eyes the central result is 
not fusion but rivalry. We perceive first one field, then the other, alter- 
nately. 



236 



PERCEPTIONS 



called surface perception. It is not the perception of blank, 
unfilled space, but our ability to appreciate the distance and 
direction of things (or of their parts) from one another. 

This type of perception is based upon the local signs of 
sensations, which are due to slight individual differences 
between each separate receptor.^ Each rod or cone in the 
retina and each touch corpuscle in the skin differs from every 
other in its constitution. Owing to these ' local ' differences 
the impulses stimulated by any receptor are slightly different 

in mode from those stimulated 
by the other receptors of the 
same sort, and this peculiarity 
of mode furnishes an indication 
of the source. This means only 
that we experience two simul- 
taneous sensations as different — 
not that we perceive directly 
how far apart they are. : 

Distance from point to point 
on the surface of the skin or 
retina may be called superficial 
distance as distinguished from 
depth, or distance away from the 
body. We are concerned only 
with superficial distance at pres- 
ent. Two separate factors serve 
to build up our appreciation of 
superficial distance. 

(1) When objects move over 
the skin or across the retina, or 
when the skin or retina shifts 
over stationary objects, any given point on the object stim- 
ulates a number of receptors in the skin or retina in regular 
order. We rarely or never experience objects jumping hither 
1 See pp. 219, 220. 




Fig, 



56. — Space Perception 
IN Touch 



Arrows indicate direction in which stim- 
ulus moves over the skin. (See text.) 



SURFACE PERCEPTION 237 

and thither in the field of touch or sight without stimulating 
the intermediate points. '^ 

Usually objects moving over the skin affect the receptors 
in a certain succession. [Fig. 56.] As they pass over the 
skin from A to L the points B C . . . K are stimulated one 
after the other in this order. D is not stimulated before C, 
nor E before D. If the object does not move over the regular 
path A B C . . . K L, it moves over some other regular path, 
such as A W X Y Z L. In other words, there is a regular 
succession in the order of stimulation of points on the skin, 
and this is true whether the object moves across the station- 



tJirtcTion of Ejo movement 

Fig. 57. — Visual Space Perception 

Dotted lines indicate path of light waves toward the eye from a single point (P) in the ob- 
ject perceived, and their refraction in the lens, focusing at a point A on the retina. Fragments 
of dotted lines, ending at B, C, D, indicate the focusing of light waves from the same point P at 
successive points on the retina as the eye turns counter-clockwise. (See text.) 



ary hand, or the hand moves over a stationary object. The' 
same is true of the eye. In Fig. 57 the eye is supposed to 
move in the direction indicated by the lower arrow; the 
retinal picture of any object (e.g., the letter P on the book) 
shifts in the opposite direction, falling successively on A, 
B, C, D. 

It follows that if a point on the skin or retina is situated 
far from the starting-point of stimulation it is not stimulated 

^ In the laboratory a jumping series may be devised by means of a set 
of lights in a dark room turned on and off in irregular order; or by a series of 
discontinuous touch stimuli. 



238 PERCEPTIONS 

immediately after the latter, but only after a large number 
of other points have been stimulated. Each regular touch 
series, A B C . . . K L and A W . . . Z L (and each regular 
visual series), occurs repeatedly in experience. These repe- 
titions establish relations of ' immediate succession,' ' long 
after,' etc., between the various local signs — relations which 
correspond more or less exactly to the superficial distance of 
individual receptors on the skin or retina. 

The retinal receptors are far more crowded together than 
the cutaneous receptors. The retinal surface is ' tremen- 
dously small ' compared with the surface of the body; yet 
there are more rods and cones in the eye than touch cor- 
puscles in the entire skin. This and our more frequent use 
of the eye has built up a finer system of space discrimination 
in sight than in touch. According to E. H. Weber ^ space 
discrimination at the center of the retina is 625 times as fine 
as on the tongue, which is one of the best developed tactile 
regions. 

(2) The other factor in perception of superficial distance 
is the kinesthetic sensations which accompany eye movements 
and movements of the various bodily members. When we 
move the eye about (as indicated by lower arrow in Fig. 57) 
the movement is accompanied by a sensation of efifort, due 
to stimulation of certain eye muscles. If the eye moves 
quickly through a large angle, A D, the muscle sensation will 
be different from that which occurs when we move slowly 
over a shorter distance, A B, even though the two move- 
ments occupy the same time. The effort in the first case wiU 
be more intense. The same is true of arm or hand move- 
ments. These muscle sensations accompanying the external 
sensations enable us to distinguish superficial distance from 
mere duration of movement. An object is perceived as 
distant from another not merely because a large number of 

^ Tactsinn und Gemeingefuhl (ed. by E. Hering), pp. 74, 86. From 
Wagner's Handwbrterbuch d. Physiol., Ill, Abt. 2, pp. 531, 539. 



SURFACE PERCEPTION 239 

other sensations intervene, but because the passage from 
one sensation to the other requires a considerable degree 
of muscular contraction.^ 

Kinesthetic sensations enable us also to distinguish direc- 
tion. In Fig. 56 the distance A X is the same as A C. So 
far as the amount of movement and effort is concerned the 
two experiences are identical. But to move the hand from 
A to X involves a different muscle (or muscle combination) 
than the movement A to C; and this means different kin- 
esthetic sensations. Each direction of movement involves 
different muscle sensations from every other. The percep- 
tion of direction is due to these kinesthetic sensations. This 
applies not merely to hand movement and directions on the 
palm, but to muscular movement in any part of the body. 
In the case of eye movements the kinesthetic factor is more 
obvious; movements up, down, right, and left are due to 
entirely different muscles, each with its own local sign. These 
kinesthetic data indicate to us the direction of the eye move- 
ment and the direction of the various points on the retina 
from one another. 

Central Mechanism. — The individual nerve fibers from 
various points on the skin gather together in the Rolandic 
region of the brain. It has been found that the fibers from 
the toes and feet terminate in the upper part of this region, 
the fibers from the face and head in the lower part, and those 
from the trunk, hands, etc., in between.^ It is not known 
whether the central terminals of the separate fibers are 
spread out in a way corresponding to the space relations of 
their respective receptors. An exact spatial reproduction 
seems highly improbable. 

The Rolandic region contains only the primary (sensation) 

1 Where kinesthetic data are lacking, the relative location of objects may 
be wrongly perceived. An advertising sign, "Gas Bills Cut in Two," seen 
at a glance, was read "Gil Bias Cut in Two." 

2 See Fig. 17, p. 48. 



240 PERCEPTIONS 

centers. The sensory fibers terminating there are connected 
by common association fibers which lead to higher (percep- 
tion) centers. The impulses which pass over these associa- 
tion tracts are summation impulses, in which the components 
are grouped in certain definite orders, so that the higher 
centers in the brain receive impressions of the ' order ' rela- 
tion, as well as of specific touch qualities, warmth, etc. The 
same is true of the eye. Impulses from various retinal points 
are conducted separately to the primary optic center and 
from there a group impulse is conveyed through association 
tracts to the higher visual center. 

When impulses summate together the resulting impulse 
undergoes modification and the corresponding mental state 
undergoes transformation.^ In spatial summation of im- 
pulses the modifications and transformations all belong to 
one general type. If we examine a number of experiences 
which differ only in being caused by spatially different 
stimuli, we find that these differences introduce a new char- 
acter or attribute — the spatial — which is not found in 
the component sensations. This may be analyzed into two 
factors, superficial distance (length and area) and direction. 
Distance and direction are independent variables in the space 
character of surface perception in the same way that color 
and brightness are independent variables in the quality 
character of visual sensation. 

There is one important difference between the space 
character and the quality character: the spatial differences 
of perception are due primarily to differences among the 
individual receptors, while the quality differences of sensa- 
tions are due primarily to differences among the stimuli 
which affect the receptors. 

To review this discussion. Perception of two-dimensional 
space relations is based upon many experiences of the same 
general sort. (1) It is due to the regular order in which 
^ Cf. ch. iv, p. 60, and ch. viii, p. 143. 



CENTRAL MECHANISM 241 

separate points on the skin and retina are successively stim- 
ulated. Each term in the ' order ' of local signs gives some 
specific distance relation; their sum-total gives two-dimen- 
sional (or superficial) space. (2) The combination of kin- 
esthetic sensations with specific sensations of sight and 
touch assists the spatial interpretation of local signs. It 
prevents errors in distance-perception due to slow and rapid 
movement. (3) Kinesthetic sensations also furnish * direc- 
tion signs ' whereby the direction of one point from another 
is perceived. (4) The transformation process is an important 
factor in building up space perception, as we shall find it 
also in the production of other mental states. 

c. Depth Perception and Projection: Visual. — A higher 
stage in the perceptual process is perception of the distance 
of external objects from our body. This type of percep- 
tion, called depth, has developed in sight far beyond any 
other sense. The normal human individual, possessed of 
two eyes, on seeing an object perceives at once how far off 
it is situated. This perception is subject to error, and our 
errors in depth perception are far greater than in surface 
perception. The moon may ' look ' only a few miles off, 
and a chasm may ' look ' far deeper than it actually is. On 
the whole, however, the depth relations which have de- 
veloped in sight correspond very closely to the depth rela- 
tions in the external world. Perception of depth is not 
based upon local signs; for the stimulus from an object a 
hundred miles off reaches the same identical rod or cone in 
the retina as the stimulus from an object a few inches away 
if the two lie in the same line from the eye. Depth percep- 
tion is due to the combination of certain non-visual data 
with visual impulses, just as surface perception is due to the 
combination of kinesthetic impulses with impulses from the 
external receptors. We may divide these non- visual data 
into two classes : uniocular and binocular factors. 

(i) Uniocular Factors. — The two eyes normally work 



242 PERCEPTIONS 

together, and this cooperation assists greatly in depth per- 
ception. But even when one eye is closed, or if its functions 
are impaired, the distance of objects is still perceived with 
fair accuracy. Several distinct data assist in uniocular 
determination of depth. 

(i) Accommodation Sensations. In examining the 
structure and functions of the -eye, we noted that the lens 
bulges or flattens according as the object which we are fix- 
ating is near by or far off. This change in the lens is ac- 
complished by a special muscle called the ciliary or accom- 
modation muscle. Its contraction or relaxation stimulates 
kinesthetic sensations. 

Any specific amount of contraction of the accommodation 
muscle yields a certain definite intensity of kinesthetic sen- 
sation. Hence, when we focus the eye for objects at a certain 
distance the kinesthetic sensation stimulated by the state of 
contraction of the accommodation muscle furnishes a datum 
for perceiving that distance. Thus the stimuli affecting any 
group of retinal points are perceived as near or far according 
to the accommodation sensations which accompany them. 

These data assist only in perceiving a limited range of 
depths. In the normal eye the lens is entirely relaxed when 
we fixate for about 6 to 10 meters (according to age) and 
there is no further change of accommodation beyond that 
limit, no matter how far off we look. The near-by limit also 
varies with age; for persons of 20 years the near-point is 10 
cm. We cannot contract the accommodation muscle suf- 
ficiently to focus the rays coming from points nearer the eye 
than this. 

(ii) Sharpness (Cleabness) of Outline. Owing to the 
density of the earth's atmosphere and the solid particles which 
it contains, objects at a distance do not show up in such clear 
outline as objects near by, and their surface differences are apt 
to be less distinct. Objects are perceived as close to us if 
they are sharply outlined; they appear far off if their features 



UNIOCULAR FACTORS 243 

are very indistinct. This is an important factor, but its data 
vary greatly and are frequently subject to wrong grouping. 
We misinterpret distances in looking through an unusually 
clear or unusually dense medium. In Colorado, mountains 
30 or 40 miles away seem only a half -hour walk distant. Ob- 
jects seen in a misty atmosphere loom up large, because they 
appear much farther off than they really are. 

(iii) Superposition. An object which is nearer the eye 
than a second object covers part of the more distant one if 
the two lie in the same straight line. Hence, when we see the 
outline of some familiar object broken into by another, the 
former looks farther away than the latter. This effect, called 
superposition, is of great use in perceiving the relative distance 
of objects, but not their actual distance. It is of no help in 
measuring depth except as other factors cooperate. 

(iv) Shadows and Shading. Unless the light falling upon 
an object strike it perpendicularly, any projection or indenta- 
tion will cause shadows upon its surface. When light strikes 
the human face from the right, the nose casts a shadow on the 
left cheek, the mouth is in shadow, etc. The shading is inter- 
preted as denoting that the various features are at different 
distances from the source of light and from the observer. This 
factor gives the finest of all depth distinctions. More than 
any other it enables us to see in perspective and in relief. The 
landscape appears to us not as an irregular surface but as a 
three-dimensional grouping of solid objects. So powerful is 
this factor that we tend to interpret the flat surface of a paint- 
ing or photograph in terms of depth. The objects project out 
and recede back from the plane of the canvas or paper^ Look- 
ing at the stage in a theater, we perceive a cottage in the back- 
ground at least two or three miles away, although we know 
perfectly well that the city street is less than 400 feet back 
of the foot-lights. 

(v) Size and Shape of Familiar Objects. When objects 
of a certain kind are all of about the same size, the size of the 



244 PERCEPTIONS 

retinal picture gives us a clue to the distance of any one of 
the class. For example, the height of grown-up human be- 
ings varies ordinarily only a few inches from an average of 
5 feet 7 inches. When we perceive a human figure standing 
or walking, if the size of the retinal picture is small the man 
looks distant, if large he looks near by. Houses differ con- 
siderably in size, but the windows and the height of each 
story are fairly uniform; we perceive the distance of a house 
accordingly. Vehicles, animals, trees, fences, and other fa- 
miliar objects afiford similar indications. 

This factor may give rise to misinterpretation of distance, 
A miniature house on the stage is perceived as a full-sized 
house in the distance. A child dressed in adult clothes ap- 
pears to be a grown man farther off. 

Not only the size but the shape of any familiar object gives 
us indications in regard to its position. Book covers are usu- 
ally rectangular; when we see a book lying before us whose 
cover has two acute and two obtuse angles we project one 
of the acute corners farther away from us than the other. 
[See Fig. 57.] Much of the perspective effect in paintings and 
pictures depends upon these data. 

(vi) Relative Motion of different parts of the landscape. 
When we travel through the country on a train or other con- 
veyance, objects near at hand pass by much more rapidly than 
distant objects. If when we are standing we move the head 
to right and left the same phenomenon occurs in lesser degree. 
In both cases we receive indications of the relative distance 
of objects in perspective from their relative rate of motion 
across the field of vision. For the normal individual this 
datum furnishes little aid to depth perception, but to one 
who depends entirely upon uniocular vision it is the most 
important factor in giving perspective to the landscape. 

(2) Binocular Factors. — Two additional factors enter into 
our perception of depth when the two eyes work together as 
a single instrument. 



BINOCULAR FACTORS 245 

(i) Convergence. When we look first at an object near by 
and then at an object some distance directly behind it, the two 
eyes do not act together in the same way as in ordinary eye 
movement. Either one eye remains fixed and the other turns 
slightly outward (that is, away from the nose) ; or both turn 
together in an outward direction. These eye movements 
are accompanied by kinesthetic sensations. The sensations 
which arise when both external muscles act, or when the ex- 
ternal of one eye acts and that of the other eye remains fixed, 
are different from the sensations which accompany the ordi- 
nary horizontal eye movements, where both eyes turn to right 
or left simultaneously. 

The phenomenon of fixating the two eyes upon a single 
point is called convergence. The kinesthetic sensations accom- 
panying change of convergence furnish indications of depth. 
They aid us. in perceiving the distance or depth of the point 
upon which the eyes are converged. To the normal individual, 
who uses the two eyes as a single instrument, this supplements 
to an important degree the uniocular indications; but its 
value is limited to distances of not more than 100 feet; beyond 
this there is practically no change in the angle of convergence. 

(ii) Binocular Parallax. If we hold a piece of cardboard 
between the two eyes with one edge toward us, the left eye 
sees one surface of the cardboard while the right eye sees the 
other surface ; the two visual fields are quite different. If we 
hold a ball near the eyes, the right eye sees a little farther 
around to the right. Any curved surface within a certain dis- 
tance from the body is seen slightly differently by the two 
eyes. 

A blind person finds difficulty in understanding why this 
double picture does not result in confusion. As a matter of 
fact, the two different visual pictures do not clash under or- 
dinary conditions; they combine together and give a single, 
definite impression. The differences between the two pictures 
merely cause the object to ' jut out ' in the field of perception. 



246 PERCEPTIONS 

This factor, called binocular parallax, adds the finishing touch 
to perception of depth. It gives the appearance of projection 
(relief) and solidity to visual objects. 

The role of binocular parallax may be studied by means of 
the stereoscope. If we look at two photographs of an object 
or landscape through a stereoscope, the resulting picture ap- 
pears flat if the two photographs are exactly alike, but it looks 
convincingly ' solid ' if the two have been taken from slightly 
different positions. 

Central Processes in Visual Projection. — The perception 
of depth involves the cooperation and combination of a greater 
variety of sensory elements than enter into surface perception. 
Some of the factors just discussed involve other operations 
than sensation. The perception of an object's distance based 
upon the size of the retinal picture involves retention of many 
past perception effects. When we perceive that a book is lying 
at an angle because the corners are distorted, the experience 
involves past perceptions of many different tilted positions. 
But the experience of depth is not an ' inference ' — it does 
not arise after the object is perceived. We perceive the size 
and the tilt at once. This can readily be verified experimen- 
tally. The immediateness of the depth experience indicates 
that the cooperating data combine with visual data before 
(or when) the impulse reaches the secondary visual center. 

The most difficult feature of the process to understand is 
how we come to have one single perception, not two, when each 
of the two eyes has a complete retinal picture of the entire 
field except the blind-spot area. This is partly explained by 
the course of the optic nerve. At the optic chiasm (Fig. 35) 
the fibers from the inner (nasal) half of each retina cross to 
the opposite side of the brain; those from the outer half do not. 
Hence the fibers from the left half of each retina terminate in 
the left side of the brain, those from the right half in the right 
side. Accordingly the two (similar) stimuli from the corre- 
sponding points in the two retinas arrive simultaneously at 



CENTRAL PROCESSES IN PROJECTION 247 

neighboring points in the visual center. Just how these pairs 
of corresponding central points are connected is not yet 
known. But that a mechanism of some sort has evolved for 
connecting them is indicated by the fact that we do see ob- 
jects singly when the eyes are properly focused.^ 

Another difficulty (which is more philosophical than psy- 
chological) is how we seem to see objects "off at a distance " 
when the perception process actually takes place in the brain. 
So far as perception is a mental state,, this is readily explained. 
The projective character, like the two-dimensional character 
of perception, is a specific kind of transformation. A ' pro- 
jected out ' quality is added to the component sensations by 
the several factors discussed above, in much the same way that 
a ' spread out ' quality is added to the sensation group in sur- 
face perception. Our projection of visual experiences means 
only that we project most of these visual pictures beyond the 
visual picture of our own body, which forms part of the visual 
field. 2 

Projection in Other Senses. — Distance perception and 
projection are more developed in the distant senses than in 
the contiguous senses, where the stimulating object lies close 
to the body. While projection is most highly developed in 
sight, it appears to a considerable extent in smell and hear- 
ing. A given odor is projected into the rose, seaweed, frying 
bacon, or other objective source of the stimulus. It is per- 
ceived not in our nostrils but in the outside object. Sounds 
are localized outside of the head and often at a considerable 
distance. 

The actual distance of odorous objects or sounds is not per- 
ceived with any such degree of precision as in sight. If we 
possess the sense of sight we usually project odors into the ob- 
jects which we see, and measure the distance of the source vis- 

^ The single perception of two corresponding points is a case of fusion. 
The same operation occurs in binaural hearing of identical sounds. 
2 See Appendix, "Perception of the External World," p. 416. 



248 PERCEPTIONS 

ually. The projection of sounds is assisted by training. Cer- 
tain sounds occur ordinarily within a certain range of intensity. 
If they are heard softer or louder than usual we localize them 
far off or near by, respectively. The muscle sense, while it 
cooperates in visual projection, does not build up a set of pro- 
jective relations of its own in normal, seeing individuals.^ 

The cutaneous senses (warmth, cold, touch) furnish a few 
independent indications of depth and projection. If we put 
our hand near a hot stove we ' feel ' the warmth in the region 
beyond, not in the skin. The same thing is observed in hold- 
ing the hand near a cake of ice. Ordinarily when this occurs 
our eyes are open and there is visual projection also. But even 
with closed eyes some temperature projection occurs. In 
touch, which is well developed for surface perception, projec- 
tion is only slightly developed. Indeed, one is apt to imagine 
that it is altogether lacking. But careful observation will fur- 
nish many instances. 

Projection in touch usually occurs when a rigid object con- 
nects the source of stimulation with our tactile receptors. 
When we write with a pen we feel the point of the pen touch- 
ing the paper. When we cut with scissors the touch sensation 
is projected to the place where the cutting occurs. When we 

^ The space perception of the blind is radically different from that of nor- 
mal man and deserves more careful investigation than it has so far received. 
The blind perceive all sides of a solid object simultaneously. They perceive 
the back or far side of things as well as the front. Their projective process 
is of a different type from ours. Miss Lydia P. Hayes of the New Jersey 
Commission for the Blind, who had been blind from the age of 8 and was 
gradually recovering sight after an operation, told the writer of the puzzling 
impression she received when first looking at a baseball. She did not recog- 
nize it at once as a sphere; it seemed "all bunched together." She had been 
accustomed to perceive all around a ball at once — not simply one half 
bounded by an edge, as it appears visually. 

Miss Hayes says: "The blind have no conception of perspective and 
convergence. I still find after several years that I think I cannot get by 
objects, and it seems as if buildings must fall upon me. Soon after the first 
operation I refused to go to the back of a restaurant because it seemed to 
me it was so narrow at the rear we could not get air enough , and was much 
surprised to be told that the room was of the same width throughout." 



PROJECTION IN OTHER SENSES 249 

walk we feel the pressure of our soles on the ground, and in 
using a cane we feel the tip of the cane where it touches the 
ground. Most singular of all, when we dig with a spade we 
feel the impact of the spade underground when it strikes a 
stone. ^ 

These phenomena indicate a general tendency in perception 
to project a sensation as far out from the body toward the source 
as the data warrant. Projection is a type of transformation 
which the sense data undergo in all combinations involving 
depth. Visual projection surpasses that of other senses be- 
cause the visual stimuli afford greater opportunity for the 
operation. The light waves are very minute, they reach the 
eye from enormous distances, and the receptor itself is so 
developed that it is capable of very fine local discrimination. 
But the projective process occurs to some extent among all 
sense data. Even our systemic sensations are projected from 
the brain centers to their source in the receptors within the 
body, and kinesthetic sensations of effort are often projected 
into objects, so that even inanimate things seem to possess 
power and strength. 

d. Apperception (Focused Perception). — When a group 
of simultaneous stimuli affect one of the external senses, some 
of the resulting sensations enter into the perception more 
clearly and vividly than others. Usually there is a ' focus,' 
comprising certain elements which are especially clear; other 
components of the perception are fairly vivid, and still others 
are quite indistinct or wholly unnoticed. This unevenness 
in the perception is partly due to differences in the intensity 
of the stimuli. A loud sound usually occupies the focus of 
perception, while very faint sounds which accompany it are 
unnoticed. A bright-colored pattern stands out prominent, 
while the dimmer background is scarcely observed at all. 

In most perceptions there is also an unevenness which 
arises during the combination process and may be quite inde- 
^ In these illustrations the word 'feel' means a state of perception. 



250 PERCEPTIONS 

pendent of the intensity of stimulation. When we look at a 
human face we do not observe clearly each individual feature. 
Probably the eyes, nose, and mouth stand out most promi- 
nent, the ears and chin and the arrangement of hair are no- 
ticed somewhat, while the curves and shading of the cheeks 
may escape attention altogether. These differences of vivid- 
ness among the elements composing the perception are not 
due to differences in intensity of the several stimuli, but 
depend upon the way in which the elementary nerve im- 
pulses are combined at the center into a complex perceptual 
state. 

This phase of the perceptual process is called apperception, 
or focused perception. It is apparently due to variations in 
the metabolic condition of the central synapses, which alter 
the intensity of some of the sensory impulses and produce 
changes of vividness in the components of the perception. 
The focusing process is popularly called " turning the atten- 
tion " to an object or to some of its details. 

In sight the apperception process is assisted by the mobility 
of the eye and the high efficiency of the center of the retina. 
Objects which stimulate the fovea give a clearer impression 
than those at the periphery, because the foveal receptors are 
more closely packed together and admit finer discrimination 
than the rest of the retina. Since we are able by an ocular re- 
flex to turn the eyes so that bright objects perceived periph- 
erally will stimulate the fovea, the foveal region of the retina 
comes to be the part most frequently used in visual percep- 
tion; its central connections are generally in the most favor- 
able metabolic condition. The popular idea of ' turning ' the 
attention is based upon this act of turning the eye, which plays 
such an important part in visual perception. 

In touch the focusing process is often assisted in a similar 
way. The finger-tips and the tongue are regions of fine dis- 
crimination; objects are apperceived by touching them with 
these members. In hearing we sometimes focus by turning 



APPERCEPTION 251 

the head, and in smell we intensify certain sensations by 
drawing a long breath. 

Apperception occurs also without these motor aids. One 
can learn to observe out of the ' corner of the eye,' so that an 
object near the periphery is attended to without turning the 
eyeball. We pick out certain agreeable or disagreeable odors 
from a mass of smell sensations. In hearing there is the classic 
instance of the doctor who is aroused at night by the front- 
door bell, while his wife sleeps calmly on; when the baby cries 
the wife jumps up and the physician slumbers undisturbed. 

The increased vividness of some components is only half 
the story. There is a ' defocusing ' as well as a focusing. In 
the grouping process some of the synapses are partly blocked, 
and the impulses along these paths lose in strength as they 
pass into the higher neuron; the corresponding portion of 
the impression is less vivid than the intensity of its stimu- 
lus warrants. The process of apperception includes both of 
these phases, focalization and defocalization, attention and 
inattention. 

A special problem in connection with apperception is the 
number of objects which can be perceived distinctly at once; 
not the total number of components in the perception, which 
may be indefinitely great, but the number of ' vivid groups ' 
which are marked off as separate objects. This is called the 
span of attention. Experimental investigations have given 
different results, and it appears that the span depends upon 
several factors. Under ordinary conditions from 6 to 8 ob- 
jects are clearly distinguished simultaneously. The number 
may be increased with practice to about 15. 

e. Object Perception. — Objects in the environment usu- 
ally affect more than one of the senses. They provide 
stimuli of various sorts which act upon several types of re- 
ceptor at the same time. An orange (which for some reason 
psychologists generally select for illustration) may affect at 
once the eye, the skin, the muscles, the nostrils, and the taste 



252 PERCEPTIONS 

bulbs. As a result we see, touch (' palp '), heft, smell, and 
taste it, all at the same time. 

Stimuli from different objects which affect different recep- 
tors usually tend to inhibit one another. When we are reading 
a book the conversation about us and other noises pass un- 
noticed, and when we listen to conversation the objects about 
us may be lost to view. But in the case of simultaneous stim- 
uli from the same object the opposite is true. The visual, 
tactile, kinesthetic, olfactory, and gustatory sensations in- 
duced by an orange combine into one single perception. This 
type of mental state is called perception of objects, or object 
perception. In discussing surface and depth we spoke of ' per- 
ceiving objects,' although only one class of receptor was in- 
volved. This is in fact the beginning of object perception; 
but perception of objects in the environment is only com- 
pletely ' rounded out ' when the mental state includes several 
sorts of data — sight, kinesthesis, and touch, for instance. 
The distinction is more important than one might realize. In 
certain pathological conditions the kinesthetic sensations are 
cut off. The patient reports that the world which he sees 
does not " look real." He lacks object perception in its high- 
est form. 

In object perception the space relations in the several senses 
dove-tail together. We feel (palp) our hand as situated in 
the same place as that in which we see it. The space data 
from the various sensory sources are integrated. Our field 
of perception consists of only one space — not a visual space, 
a tactile space, and a kinesthetic space. This is brought out 
strikingly when the normal relationship of the senses is dis- 
turbed. If we look at our hand through a reversing lens we 
feel the fingers in a different place from where we see them. 
In using a microscope we push the slide in one direction to 
produce visual movement in the opposite direction. 

Reintegration of perception under abnormal conditions 
was observed in Stratton's experiment. Stratton wore a 



OBJECT PERCEPTION 253 

large reversing lens continuously for 7 days, removing the 
apparatus only at night, when the eyes were bandaged. The 
whole field of vision was thereby turned 180° from the normal 
orientation. With respect to touch and muscle sense his left 
hand was seen at the right side, his feet above, the lintel of 
a door was seen below. At the end of the period he found that 
the space relations were at times almost completely rein- 
tegrated to meet the new conditions. He reached for things 
where he saw them and manipulated implements properly. 
He felt his hands, feet, and body in the same place and in 
the same relations as their visual pictures. Only the head, 
which had not been seen during the experiment, remained 
partly in the old tactile situation; — its localization was con- 
fused and vacillating.^ 

The neural mechanism for object perception is the numer- 
ous tracts of nerve fibers which connect the various sensory 
centers in the cortex. These association fibers make it pos- 
sible for simultaneous impulses in different centers to pass to 
some common higher center and combine together there. 

The development of object perception depends upon fre- 
quent repetition of similar combinations of sensory impulses. 
If a certain visual impulse is accompanied by various tactile 
or auditory impressions at different times, there is no fixed 
mode of combination between them; but where a certain vis- 
ual perception (e.g., an orange) is always accompanied by sim- 
ilar olfactory sensations, similar touch sensations, etc., their 
combination into a definite sort of perception becomes more 
and more fixed. In other words, object perception begins 
with the most common objects about us, and develops con- 
stantly as our habitual experiences extend to a greater variety 
of things and beings. 

^ The oldest recorded piece of work in experimental psychology, Aris- 
totle's experiment, is in the same general field. Aristotle noted that if the 
middle fingers are crossed and a small object be placed between them (the 
eyes being closed) the object appears double. 



254 PERCEPTIONS 

Object perception is usually accompanied by certain idea- 
tional data in addition to its sensory components. Our per- 
ception of an orange commonly includes a taste component, 
even when the orange is uncut; iron ' looks heavy,' while alu- 
minium ' looks light.' These ideational components are due 
to the fact that corresponding taste or kinesthetic sensations 
have in the past frequently accompanied visual sensations 
similar to those now present. In adult life practically all of 
our perceptions of objects are tinged with imagery due to past 
experiences. An ' object experience ' includes the various 
impressions which we receive or have received through the 
several senses from this object or from objects like it. 

The retention factor plays an important part in the forma- 
tion of object experiences. It is due to the persistence of past 
effects that habitual sensations combine more readily than 
isolated sensations, and that ideas unite with present sensa- 
tions. Modification is also an important factor in determin- 
ing the quality of object perception. The same object or 
group of objects appears different after it has been repeatedly 
perceived. An example of this may be readily observed if 
one has been living in a new town for three or four years. 
Apart from any changes which have actually taken place in 
the buildings or landscape, his perception of the place is quite 
altered; the difference is due to the growth of new object per- 
ceptions, and especially to the modifications produced by 
ideational elements of the * memory ' type. 

In certain individuals a peculiar type of object perception 
occurs, in which ideational components of an arbitrary sort 
enter into the mental state. These persons report that cer- 
tain sounds assume a pronounced visual tinge. One vowel 
sound looks blue, another red, etc. According to the reports 
these mental states are perceptions, not merely ideas which 
follow perceptions. The experiences are sometimes called 
colored hearing; but similar perceptions occur in which other 
senses are involved, so that this type of object perception is 



OBJECT PERCEPTION ^55 

more properly termed synesthesia. Synesthesia Is probably 
due to certain chance groupings of sensations which occurred 
early in life and have persisted in spite of their lack of basis 
in external stimulation. These phenomena are not patho- 
logical, but on the other hand they are not in line with the 
ordinary development of object perception. 

f . Perception of Time, Rhythm, and Events. — Most stim- 
uli persist for some length of time, and the sensations which 
they produce persist also. When an object moves or changes 
or disappears, the impulses in the higher centers do not im- 
mediately cease nor alter all at once; there is usually a certain 
period during which the old perception is fading away and 
the new perception is beginning. In other words, successive 
perceptions dove-tail together; we perceive at one and the 
same instant both the in-coming and the out-going events. 
The ' now ' of perception is not the same as the physicist's 
conception of the ' present.' It is not a thin knife-edge sepa- 
rating the past from the future, but a fair-sized interval of 
time. 

According to careful experimental investigation the per- 
ceptual present (sometimes called the ' specious present ') is a 
duration of about 6 seconds (Titchener). All impressions 
within this period of time are present to us at once. This 
makes it possible for us to perceive changes and events as well 
as stationary objects. The perceptual present is supple- 
mented by the ideational present. Through the combination 
of perceptions with memory images (ch. xiii), entire days, 
months, and even years of the past are brought together into 
the present. Thought (ch. xv) extends our present experi- 
ence still further to include centuries and eons of time, both 
past and future. 

The gradual appearance and gradual fading away of per- 
ceptions form the basis not only of our experience of events, 
but of our experience of duration. As a perceptual experi- 
ence, the range of each of these periods is very limited. The 



^56 PERCEPTIONS 

generalized experience of time relations (often called time per- 
ception) is not a matter of perception but of thought. 

The unevenness of successive experiences gives rise to a 
special type of perception called rhythm. Rhythm occurs al- 
most exclusively in connection with auditory data. It is due 
to the succession of more vivid and less vivid perceptions. 
These group themselves into a series consisting of accented 
and unaccented elements, which occur alternately. The accen- 
tuation (or vividness) is generally due to some character of the 
stimulus. In poetry or music the accented syllable or beat 
is made prominent either (1) by greater intensity (loud, soft, 
soft, loud, soft, soft), (2) by longer duration (J J j J J j)' 
or (3) by some specific quality; if the bass is C, E, E, C, E, E, 
this serves to accentuate the first and fourth clangs. Two 
or more of these factors often cooperate to produce rhythm, 
and at times the rhythm may be due partly (or entirely) to 
central factors. One may readily weave a rhythm pattern 
into the uniform ticking of a clock. The rhythm experience, 
like the generalized experience of duration, usually involves 
imagery or thought. 

A number of different tones or clangs, arranged in rhythmic 
series, are grouped together into a perceptual unit called a 
tune. A familiar tune, such as the Star-Spangled Banner or 
the Marseillaise, comes to have an individuality of its own. 
Our experience of one tune differs from that of another in 
much the same way as our perception of a table differs from 
that of a chair. The growth of this individualizing process 
may be readily observed. When one first hears the army bu- 
gle calls they appear as mere tone-successions, only vaguely 
differentiated from one another. After a time the tattoo, 
reveille, and others come to be as distinctly individual as the 
familiar visual objects of every-day life. 

Series of data from the other external senses, especially 
sight, are grouped together in a similar way. Familiar acts 
which we see others perform consist of a succession of visual 



TIME, RHYTHM, AND EVENTS 257 

sensations, but they are perceived as single events. Such, for 
instance, are walking, running, stooping, eating, speaking, 
gesticulation. In the same way the fall of a leaf, the turning 
of a wheel, the lashing of surf, and all the various activities of 
animate and inanimate nature are perceived as events. 

There are more ideational components involved in event 
perception than in object perception. The experience of 
present objects consists almost wholly of sensations, while 
event experience includes more and more of imagery as the 
period of time involved is lengthened. When we see some 
one smile our perception is altogether sensory; in our per- 
ception of a horse-race the sensations toward the end are in- 
terwoven with many memories of the preceding stages. In 
every case the basis of the experience is sensory; the mental 
state is perceptual. 

g. Perception of Differences (Discrimination). — Simple 
motor discrimination does not involve the activity of higher 
nervous arcs. An impulse may be distributed directly into 
various motor paths through the lower centers. Even a re- 
flex may give a discriminative response. But the type of 
discrimination which we observe subjectively is a perceptual 
state; its arc goes through the higher centers. 

When we perceive differences of intensity or quality between 
two sensations, the two sensory impulses are brought together 
in a perception center and the distribution of the motor im- 
pulse is regulated by the intensity or mode of the sensory 
impulses. If we compare the intensity of two sounds our mo- 
tor response is the spoken word ' louder ' or ' softer ' (or some 
equivalent pair of responses) , Which word we utter depends 
upon the order in which the two stimuli are presented. The 
neural operation in the centers is discrimination, or percep- 
tion of difference. Two perceptions may be discriminated not 
only as to quality and intensity, but in respect to duration 
and extensity, 

A large part of the experimental work in psychological lab- 



258 



PERCEPTIONS 



oratories has been concerned with perception of differences. 
Almost all of the investigations in psychophysics, which are 
summed up in Weber's Law/ use perceptions for their ma- 
terial. 

Table XIV shows the values of the discrimination con- 
stant for intensity in the several senses as determined by ex- 
periment. The fractions indicate in each case that the in- 
tensity of the stimulus must be increased by that proportion 
of itseK to produce a " just perceivable difference." This 
fraction is called the limen or threshold of difference for the 
given sense. Fig. 58 shows the increase in the stimulus for 
each ' step ' in the perception of differences of noise intensi- 
ties. The curve for touch is similar in form but flatter; the 
muscle sense curve is flatter still; the visual curve is flattest 
of all. The flatter the curve, the finer is the discrimination. 



Table XIV. 


— Values of the Webeb Constant 


Sensation 


L.P.D. Intensity 


Individual range 


Visual (light) 


0.01 

0.33i 

0.15 

0.25 

0.25 

0.05 

0.33i 

0.33i 

0.025 


015 to 0.005 


Auditory (noise) 

(tones) 

Olfactory 


0.20 to 0.125 
0.33 to 0.25 


Gustatory 


33 to 25 


Tactile 


10 to 033 


Warmth 


. 33 to . 25 


Cold 


0.33 to 0.25 


Kinesthetic 


. 05 to . 013 







Each fraction denotes the proportion of the original stimulus which must be added to it in 
order that the sensation may be just noticeably greater. 

The just perceptible differences of color hues and auditory 
tones may also be determined experimentally. Their values 
are expressed in terms of the wave lengths of the stimuli. 
They do not follow the Weber Law. 

Truth and Illusion in Perception. — Our perception of the 
qualities and relations of external objects and events is far 
* Cf. chs. V, xi. 



PERCEPTION OF DIFFERENCES 



259 



Pig. 58. — Curve of Weber's Law 

Form of the curve for intensity of sound; constant = i. Successive "just per- 
ceptible" increases of sensation are indicated by equal distances along the X 
axis at points Si, S2, etc. Corresponding values of stimuli are represented by the 
lines Si — Rj, Sj— Rj, etc. 



260 



PERCEPTIONS 



more exact than would be expected from a consideration of 
the sensory data. The fact that the visual receptors are 
located in one region, the auditory receptors in another, the 




Remarkable 

Truly is Art ! 
See — Elliptical 

Wheels on a Cartl 
It Looks Very Fair 
In the Picture, up There, 
But Imagine the 

Ride, when you Start! 



Fig. 59. — A Study in Perspective 

The cart-wheels appear circular, though they are actually drawn as 
ellipses. The smaller sketches show what would happen if the wheels 
were really elliptical. [From Gelett Burgess.] 

taste bulbs in a third, might lead one to suppose, if he had no 
senses of his own, that a human being would see things in one 
place, hear them in another, and so on. The complicated 




TRUTH AND ILLUSION IN PERCEPTION 261 

paths of the nerve fibers to the brain and the separation of the 
various sense centers would serve to confirm this supposition. 
But as a matter of fact we normally project all the various 
sense data from any given object into the same set of space 
relations. We perceive it as one object, not many. 

It is certainly not remarkable, considering the intricacies 
of the perceptual process, that the outcome is sometimes in- 
exact — that our mental states do not always present the 
true relations of objects in the environment as determined 




Fig. 60. — Staihcase Illusion 

At first sight this appears to be a flight of stairs. It can be 
reversed by focusing on the upper jagged line, so that the upper- 
right corner appears nearer than the lower-left; the figure then 
looks like a cornice, or like cellar stairs seen from underneath. 
[From Jastrow.] 

by physical measurements. Perceptual grouping is based 
upon habit, and when present sensory data conflict with 
firmly established types of experience an ' untrue ' perception 
arises.^ A perception which does not correspond to the situ- 
ation in the environment is called an illusion. 

^ Philosophers have worried considerably over the 'truth' and 'falsity' 
of sensation and perception. The psychologist does not regard this as a 
distrubing problem at all. From external object to perception there is a 
long road to travel — first the stimulus, then the sensory impulse, the sensa- 
tion, and the grouping of impulses. If there is a defect in any portion of the 
pathway, the percepton is affected. All perceptions are more or less ' untrue ' 
— they are not 'copies' of the external objects — they represent objects 
imperfectly at best. 



262 



PERCEPTIONS 



Some familiar illusions have already been noted: on a misty 
day objects look larger or farther oflf than they actually are; 
a well-drawn * jflat ' picture is seen in perspective. 

The wheels of a real cart are not elliptical as shown in Fig. 




Fig. 61. — Illusion of the Cubes 

Either .six or seven cubes are seen, according to the perspective. 
[From Jastrow.] 



59; we perceive both real wheels and pictured wheels as cir- 
cular. In some cases the perspective interpretation of a pic- 
ture is variable; sometimes one point in the jBeld appears 
nearer, sometimes another. Two examples of this, the stair- 
case and cube illusions, are given in Figs. 60 and 61. 

Certain illusions show the influence of the various factors 
which cooperate in the perception process. In Fig. 62 the 
outline of the letters is completed by ideational elements. 
(Observe the effect of turning this figure upside down.) In 
the footnote on page 261 are two misprints which many 
readers will overlook. 

Pig. 63 illustrates the conflict of inconsistent interpreta- 
tions; we may see the creature either as a duck or as a rabbit. 



TRUTH AND ILLUSION IN PERCEPTION 263 

A well-known type of illusion is the puzzle picture, in which 




Fig. 62. — Filled-in Perception 

Hold the book at a distance and the outline of the letters appears 
complete. The missing lines are supplied in perception. 

some object is obscurely outlined among the more prominent 
features of the drawing. Once the ' hidden ' object is per- 




FiG. 63. — Double Perception 

The rabbit-duck. [From Jastrow, after Harper's.) 



ceived it tends to become focalized. Fig. 64 appears first to 



264 PERCEPTIONS 

be an ordinary diagram of the brain; later the "children of 
the brain " become the center of attention. 



\ 



^ 



Pig. 64. — Hidden Perception 

Children of the brain. [From Titchener, after Gudden.J 

Certain illusions are due to eye movements which are not 
properly taken into account in perception; the kinesthetic 
data furnish a report of the actual eye movements, which are 
greater or less than the distances they are supposed to cover; 
to this extent the perception does not tally with the external 
object or event. Many illusions of this sort have been dis- 
covered. Two examples are given in Figs. 65 and 66. In tbn 
Miiller-Lyer illusion the left distance is perceived as con- 
siderably longer than the right, though the two are really 
equal. In the Hering illusion the two horizontal lines are 
really parallel, but they are perceived as ' bow-legged.' 
In the Miiller-Lyer figure the eye travels not from apex to 
apex, but from some point within the first angle to a cor- 
responding point within the second angle, making one dis- 
tance appear longer than the other. In the Hering figure 
the eye is diverted from a straight path by the converging 



TRUTH AND ILLUSION IN PERCEPTION 265 

cross-lines, making the horizontal lines appear to curve in 
the opposite direction. 

We may mention here the effect of changing the orienta- 
tion of objects, though this is not so much an illusion as a 




<> 



Fig. 65. — Muller-Lyer Illusion 

Distance between apex of left and apex of central figure appears longer 
than between central and right. The two distances are equal. 

measure of the direction factor in surface perception. An 
imsymmetrical building or landscape in a reversed photo- 
graph does not look strange unless we are very familiar with 




Fig. 66. — Hehing Illusion 
The horizontal lines appear to bend apart in the middle. They are paralleL 

that particular building or scene. Human beings and ani- 
mals (being usually symmetrical) are easily recognized in a 
' mirror-picture.' But reversed lettering, especially ' mirror- 
script,' appears a fantastic jumble. [Fig. 67.] This is due 
to a special factor of asymmetry in the mental operation of 
reading.^ A curious change in perception occurs if we look 
at the landscape with the head upside down. 
^ See ch. xv. 



266 PERCEPTIONS 

Relation of Perception to Sensation. — We are now in a 
position to distinguish between perceptions and sensations. 
Perception, like sensation, depends upon present stimulation 
of the receptors; its chief components are derived from the 
external senses, and its characters are determined originally 



-.^l^S<> 




n «a t r - w t^^ 



v,:^^-^ ^ ^_::^ :k V.t^ ^^^ .^-^ 

Fig. 67. — Perception of Mikror Script 

Unless one is practiced in reading reversed writing, it is difficult to recognize a 
single word in the above. Hold it tO' a mirror and the writing is quite plain. 

by the quality and intensity of the stimuli. To this extent 
sensation furnishes the basis for the perceptual processes. 

But in addition to its sensory components perception de- 
pends upon several central factors : 

(1) Summation of many separate impulses into one; that 
is, the combination (fusion and colligation) of separate sensa- 
tions. 

(2) Metabolic changes in the separate impulses ; that is, the 
operation of a focalizing factor which produces vividness in 



RELATION OF PERCEPTION TO SENSATION 267 

certain components and obscurity in others, often quite out 
of proportion with their sensory intensity. 

(3) Modification of the resulting impulse; that is, a trans- 
formation of quality due to the mutual interaction of the 
components, including the ideational components which 
enter into the perception. 

In all these respects perceptions are determined less by the 
specific stimuli and more by the central mechanism than sen- 
sations. Yet as we have noticed, perceptual states corre- 
spond more closely to the ' general situation ' in the outer 
world than their components.^ 

The two characters of sensation, (1) quality and (2) in- 
tensity, are carried over to perception. In addition, per- 
ception has three characters of its own. (3) Vividness, a 
quantitative variation which is independent of the stimulus 
and is due to the central focalizing process, or attention. (4) 
Extensity, due directly to the grouping together of impulses 
from separate nerve fibers on the basis of local signs, and 
indirectly to the space relations of external objects. (5) 
Duration, due to the prolongation of stimulation and of 
the nerve impulse. 

Physiology of Perception. — The manner in which sense 
data are combined into perceptual experiences depends 
primarily upon the inherited structure of our central nervous 
system. Sensory neurons which lie near together in the 
brain and connect up with a single higher neuron, tend to 
furnish group impressions. Thus a number of visual sen- 
sations which occur simultaneously may be joined together, 
forming a single mental state which is very like a sensation. 
The same is true of auditory impressions and other types. 
The sight of a red disk, the sound of a complex chord, belong 

^ Perception does not remove all the distortions which the stimuli 
undergo in their path from the source to the receptor. A stick partly 
under water appears bent at the water-line; the two rails of a track 
appear to converge toward the horizon. These are not illusions of percep- 
tion, but uncorrected stimulus-illusions. 



268 PERCEPTIONS 

to the simplest type of perception; the grouping probably 
takes place in the primary centers. Perceptions which in- 
volve various senses are brought about by the operation of 
association fibers which gather the separate data from sev- 
eral centers into a higher center. This results in perception 
of objects. 

The perception of space relations develops because im- 
pressions from different local receptors usually occur in 
certain definite sequences, and because these sequences are 
distinguished by certain kinesthetic accompaniments. Both 
surface perception and depth perception are built up in this 
way. 

Both the grouping process and the familiarity coefficient 
are due to retention traces in the central neurons, which have 
been consolidated by frequent repetition of similar per- 
ceptual experiences. In adult life our perception of every 
common object and event is something more than an ex- 
perience of the present sense data; the central state is con- 
solidated and supplemented by data from past experiences. 
Our perception of a friend's face when we observe it in full 
front, includes a vague impression of his profile and the 
back of his head. The more frequently we observe the same 
object or occurrence with slight variations, the fuller and 
richer does our perception of it become. Absence of these 
ideational components hampers the perception process, as 
illustrated in reversed handwriting. 

The highest development of perception, then, depends not 
only upon the presence of a mass of association fibers con- 
necting the various sensory centers in the brain, but upon 
the formation of specific connections by means of these 
fibers, and the retention of such effects. 



Collateral Reading; 

Titchener, E. B., Textbook of Psychology, sees. 85-104. 
Breese, B. B., Psychology, ch. 9. 
James, W., Psychology, chs. 20, 21. 



PHYSIOLOGY OF PERCEPTION 269 

Witmer, L., Analytical Psychology, chs. 1-4. 

Ladd and Woodwort.h, Physiological Psychology, Part II, chs. 4, 5. 

Judd, C. H., Psychology, General Introduction (2d ed.), eh. 8. 

Angell, J. R., Psychology, chs. 6, 7. 

Pillsbury, W. B., Fundamentals of Psychology, chs. 8, 9. 

Ogden, R. M., Introduction to General Psychology, ch. 11. 

Mellone and Drummond, Elements of Psychology, ch. 12. 

Myers, C. S., Textbook of Experimental Psychology (2d ed.). Part I, 

chs. 19-23, 25. 
Mach, E., Contributions to the Analysis of the Sensations (trans.), pp. 

41-150. 
Buehler, K., Die Gestaltwahrnehmungen. 

Pierce, A. H., Studies in Auditory and Visual Space Perception. 
Stratton, G. M., Experimental Psychology, ch. 7; and Psychol. Rev., 1897, 

4, 341-360, 463-481. 
Scripture, E. W., The New Psychology, chs. 10-13, 

Practical Exercises: 

Examine how far your depth perception depends upon each of the eight 
factors mentioned in the text. 

Test the 'staircase illusion,' i.e., eye movement, volition, time, etc., in 
changing from one perspective to the other. 

Glance for one second at a shop window as you walk by. What objects 
did you perceive .'' Repeat for several shops and note number of per- 
ceptions obtained for each. 

Analyze the perception of an apple into its components. 



CHAPTER XIII 

PRIMARY MENTAL STATES (continued) 
2. Imagery 

Natixre and Classes of Imagery. — An image consists of 
groups of ideational elements. The grouping of component 
ideas into an image is similar to the grouping of sensations 
in perception. The quality of an image is not determined by 
the mode of present sensory impulses ; it is determined by the 
retention trace. 

Images are divided into two main classes, according to the 
nature of their components. "^ (1) Images in which the chief 
components are traces of former sensations. These are called 
memory images. (2) Images in which the components are 
modified traces. These may be grouped together as synthetic 
images, but they really comprise several distinct kinds, dif- 
fering according to their relation to the environment. Alto- 
gether we find the following classes of imagery: 

Memory images 
Free images 
Anticipation images 
Imagination images (fancies) 
General images 

We shall find later that imagery develops in man into a 
higher type of experience called thought. Psychologists often 
group together the various types of experience based upon 
external sensations — perception, imagery, and thought. 
They are called the intellectual functions, or cognition. While 

^ The term image is often used rather loosely. An after-sensation is im- 
properly called an after-image. The retinal picture is frequently called 
the retinal image. In popular usage imagery is applied almost exclusively 
to visual imagery — leaving tactile, kinesthetic, and auditory imagery en- 
tirely out of account. 



NATURE AND CLASSES OF IMAGERY 271 

it is important to recognize the relationship between the ex- 
ternally derived mental states, due to their common origin, 
the name should not lead us into assuming that a special 
' cognitive faculty ' exists. 

a. Memory Images. — The popular notion of memory is 
based upon too close an analogy with perception. Objects 
in the environment continue to exist even when we do not 
perceive them. Popular psychology assumes that ' memory 
objects ' (memory images) persist in much the same way. 
It is true that something remains in the brain after the sen- 
sation ceases, which furnishes the basis for future memory 
images. But what remains is not a ' picture ' of the object 
or event, but merely a record; i. is a trace or set or retention 
effect of some sort in the strurture of the neurons or synapses. 
This trace does not resemble the object, nor is it like the 
sensation. It is somewhat analogous to a phonograph record, 
where the tracings bear no resemblance whatever to the words 
or music, but bring about a reproduction of these effects when 
the needle and diaphragm are properly applied. 

Even when this trace is re-excited the result is not always 
a memory image. If the new impulse is intense when it 
passes into the higher central neurons the structural trace 
merely adds one more component to the perception. An 
example of this is the taste which accompanies the percep- 
tion of an uncut orange. When the same complex stimulus 
is repeated several times, the effect is not to transform the 
perception into an image, but to modify slightly the present 
perception. This slight modification is called the feeling of 
familiarity. We observe it when we see some person or some 
building over and over again. In such cases the mental 
experience of familiarity is not a feeling but an ideational 
component in the perceptual state. 

The memory image is a definite reproduction of some past 
experience. It is presumably caused by a central impulse 
entering a higher neuron (or group of neurons) in which a 



272 IMAGERY 

complex trace has been left by former experiences. If the 
mode of the new impulse is transformed by the set of this 
neuron a memory image results. A memory image is more or 
less complex. It may include some sensory components in 
addition to the ideational. When I recall some event I may 
feel elation or regret, which were not part of the original 
experience. These sensory components are due to present 
systemic stimuli whose impulses are combined with the 
ideational components. 

The older psychology distinguished four factors in mem- 
ory : retention, recall, familiarity, and time and space location. 
Retention is a characteristic of nerve structure; it is a con- 
dition of memory in precisely ^he same way that the receptor 
is a condition of sensation. Recall belongs not merely to 
memory but to all types of imagery; it is a picturesque name 
for the ideational process itself. Neither of these factors is 
especially characteristic of memory. The fact that they 
were considered so by investigators trained in self-observa- 
tion shows how necessary it is to check up self-observation 
by means of physiology. 

Location in time and space means that the image is ' placed ' ; 
a memory image carries with it enough contiguous elements 
to enable us to fit it into a certain period in our past exper- 
ience, and into a certain environment. This is characteris- 
tic of memory. The temporal location is a different process 
from the spatial. I recall the spot where I stood near the 
Capitol when President-elect Wilson drove up with Presi- 
dent Taft to be inaugurated. I recall the procession and the 
crowds, even to the woman standing on the corner with three 
small children. These are part of the memory image. The 
more elements it contains, the more definite is its ' space 
location.' 

The temporal location is an ' afterthought.' I place the 
incident on March 4, because presidential inaugurations 
occur on that date. If the image is a memory of my last 



MEMORY IMAGES 273 

meeting with some friend, the vividness of the image assists 
the temporal identification. In general among civilized men 
the scheme of dates represented by the calendar is the chief 
factor in determining the time relation; and this involves 
the thinking process. 

An image is recognized as memory when the feeling of 
familiarity attaches to it. If the impulse passing into a 
certain neuron brings with it no mode different from that 
of the retention trace, the passage through that neuron is 
attended with greater ease than if the new impulse alters the 
mode of the retained trace. That is, a ' revival ' of the pre- 
vious trace without change is accompanied by a familiarity 
coeJSScient. 

The presence of a familiarity coefficient in the memory 
image does not always indicate that the image corresponds 
to a previous sensory experience. The recollection may 
revive an earlier imagination as well as a former sensation. 
The memory image of any earlier image is characterized by 
familiarity. We may have vivid imagery of certain family 
incidents of childhood which have been told us repeatedly; 
when we recall them in later life, they often appear to be 
memories of the events themselves; yet we sometimes dis- 
cover that we were not present on the occasion, or even that 
they occurred before we were born. 

Such misinterpretations of the familiarity coefficient lead 
to illusions of memory. Another type of memory illusion 
occurs when two memories are combined in one; we remem- 
ber a remark and attribute it to the wrong person, or we 
associate some occurrence with the wrong time, place, or 
general setting. The line between sensation and memory 
image is not sharply drawn when the stimulus and sensation 
fade gradually away, especially if an after-sensation follows 
the sensation. When we look at a bright object and then 
look away, an after-sensation often appears (ch. ix). After 
this has faded away a similar memory experience may still 



274 IMAGERY 

persist. We are not always certain in such cases at what 
moment the after-sensation ceases and the memory image 
begins, though a trained observer can usually distinguish 
between the two forms of experience. 

In man the cultivation of the imagery life has developed 
a ' temporal perspective ' more or less analogous to the space 
perspective of perceptual experience. Our past life presents 
itself as a continuum in time, extending (or ' protending ') 
from the present moment to our earliest years. Any memory 
image which occurs at the present moment is projected back 
to some point in the series. Like space projection this proc- 
ess depends upon certain indications in the present experi- 
ence. The familiarity coefficient is an important factor in 
effecting the projection. Another factor in adjusting the 
time perspective is the nature of the specific image, which 
' fits in ' better with one period or date than other. The 
perfection of temporal perspective as a general scheme de- 
pends upon successive association.^ Illusions of wrong 
projection occur frequently in memory. A vivid memory, 
such as a great flood or the death of a brother, is placed too 
close in the foreground. A changed situation in life, such as 
moving to a new town or starting in a profession, is soon 
thrown back too far into the past. Many such instances 
of mistaken memory perspective occur in the experience of 
everyone. 

b. Free Images. — A free image is an image which lacks 
definite reference to a specific time, space, and setting. We 
may picture the face of a friend or a tune which we have 
heard, without special reference to the time and circum- 
stances in which the original perception occurred. Usually 
the free image results from frequent repetition of sub- 
stantially the same experience. The effect of this repetition 
is to weaken the general setting, which is different in each 
case. The feeling of f amiharity on the other hand is strength- 
^ See ch. xvi. 



FREE IMAGES 275 

ened. A further effect is to enrich the character of the image. 
The free image of a friend's face usually includes profile and 
full front, and the free image of our house may include both 
inside and out. The free image, then, has many of the 
characteristics of the memory image, including the familiarity 
feeling, but it is not a reproduction of one single experience. 

c. Anticipation Images. — A free image may be compli- 
cated by a ' prospective reference,' that is, it may be asso- 
ciated with some future time and circumstances. It is then 
called an anticipation image. Genetically, we find that the 
anticipation image appears before the memory image. 
Imagery seems to have been used in the first place as a means 
of adaptation to future conditions, and not as a means of 
recalling and picturing past occurrences. When a baby 
cries for milk there is probably a faint anticipation image 
present. In the adult, however, both memory and free 
imagery attain greater importance. The familiarity feeling 
is not altogether lacking in the anticipation image, for the 
free image enters largely into its make-up; but this famili- 
arity feeling is much weaker than in the types previously 
described. 

d. Imagination Images (Fancy). — The imagination im- 
age, often called constructive imagination, is an image com- 
posed of two or more distinct elements — usually a great 
number. The free image and the anticipation linage might 
be regarded as varieties of imagination; but these types are 
based upon original stimuli derived from single objects or 
events, while imagination images are composite. They are 
derived from a number of separate sensory stimuli, due to 
different external objects or events. A typical illustration 
is the image of a centaur, which combines the head of a man 
with the body and legs of a horse. Here the new experience 
is obviously derived from two separate perceptions — unless 
it happens to be the memory of a picture we have seen. The 
scenes in a novel as we picture them are imagination images. 



276 IMAGERY 

and so are the earliest plans of an inventor. Imagination 
images are often called fancies. 

There is no hard and fast line separating imagination from 
anticipation imagery. A fancy which is likely to be realized 
may be regarded as an anticipation image; and when a so- 
called anticipation is not fulfilled it is classed as a fancy. The 
distinguishing mark of imagination is the absence of the 
familiarity feeling; but even this is not an absolute criterion, 
for the constituent parts of the image are familiar, and if the 
entire imagination image is repeated, a familiarity feeling 
gradually attaches to it. The only psychological justifica- 
tion for distinguishing imagination as a separate sort of 
imagery is that it has no direct relation to our motor activity 
and to the production of changes in our environment. 

It might seem indeed as though the anticipation image 
were merely an outgrowth and specialized form of imagina- 
tion. But genetically there is little doubt but that antici- 
pation arose earlier than imagination. The several forms of 
imagery develop only as they serve to mediate between the 
creature and his environment. The human child develops 
anticipation imagery, with its motor components, some time 
before pure imagination. 

e. General Images. — A general image results from the 
fusion of many similar images into a single experience. In 
free imagery we have a combination of similar experiences 
due to the same stimulating object. The general image 
arises from stimulation by a number of objects which are 
partly similar and partly unlike. Having seen a number of 
men whose general appearance is the same, but who present 
certain differences, the child forms an image which is a sort 
of composite picture of them all. Their common points are 
present in the focus of the image, some of the different de- 
tails may appear in the margin. In the same way the general 
image of a horse is formed when the child has seen a number 
of different horses; and so for any class of objects. 



GENERAL IMAGES 277 

In adult life the general image is rarely present in pure 
form. Almost always a word or symbol of some sort at- 
taches to it. The experience then belongs to a higher type 
of experience, thought.^ The general image or composite 
picture precedes thought, and occasionally persists in later 
life if no word has been conventionally attached to a certain 
experience. 

We can investigate the general image by examining a 
thought and eliminating the verbal symbol. Take for ex- 
ample the general image of horse. The image which we have 
(lea\'ing out of account the name horse) is usually based upon 
some one specimen; it may be an old chestnut mare which we 
saw frequently in childhood. Attached to this are a variety 
of differing characters, such as gray and black, long tail and 
bobtail, stocky and slim, derived from experiences of other 
horses. These enrich and round out the image in much the 
same way that the associated elements round out the free 
image. They are often exceedingly faint, and many details 
which characterize the original perception are lacking alto- 
gether. In other words, our general image of horse, though 
based upon some particular animal, is not stocky nor slim, 
it has no distinctive color, etc.; many of the outlines and 
features which exist in all horses are wanting. The dominant 
components in the image are those details in which all horses 
agree, and which mark them off from other creatures. 

Physiology of the Image. — The nature of the neural proc- 
ess which produces imagery has already been described 
under ideation. It is supposed to consist in the re-excitation 
of a neuron which has received a retention trace from past 
impressions. If the new nerve impulse is powerful, it is but 
slightly altered by this trace, and the result is a perceptual 
experience bearing an ideational component. But if the 
new impulse is weak when it passes across the synapse, it 
loses its own specific mode and the experience takes on the 

* See eh. xv. 



378 IMAGERY 

quality corresponding to the trace. In the latter case the 
intensity of the experience is far less than that of the original 
sensation, but it may be quite as vivid and distinct. The 
distinction between the several classes of imagery depends 
upon different sorts of grouping of the components, upon the 
importance of the sensory components, upon the presence of 
kinesthetic coefficients, and upon ease of neural operation, 
or familiarity. 

Role of Imagery in Mental Life. — The relative importance 
of imagery in the life of an individual depends largely upon 
his training and general situation of life. At any given in- 
stant a perception or other sensory state may go over into 
a memory image or some other type of imagery if the sensory 
stimulus is weak and the retention trace is strong. But the 
proportion of image states to the total mental states varies 
with one's habits of life. In some individuals we observe a 
strong tendency to live in the past or in their own thoughts 
and ideas; in others the ideational life is meagerly developed. 

The production of one image rather than another depends 
in part upon the specific stimuli which affect us at the time, 
and partly upon the strength of past experiences. The se- 
lection of material depends, in the case of memory, upon the 
three factors of recency, intensity, and repetition.^ (1) If, for 
instance, we record as carefully as possible all our memories 
during one day, it is found that the greater part are recol- 
lections of recent events, and that the number decreases as 
a function of the temporal remoteness of the original ex- 
perience. (2) More intense or more vivid experiences are 
recalled in greater number than those which were originally 
faint. (3) Frequently recurring experiences are recalled in 
greater number than isolated experiences. 

The successful training of memory and imagination de- 
pends upon following the principles of acquisition and fix- 
ation (ch. vii). It is scarcely necessary to emphasize the 
^ These factors will be treated in ch. xvi. 



ROLE OF IMAGERY IN MENTAL LIFE 279 

great practical importance of memory in modern civilized 
life, and the value of cultivating it. 

3. Feelings 

Nature of Feeling. — A feeling is a mental state whose 
chief components are systemic sensations.^ The data of 
feeling are furnished either by the pain nerves or by the or- 
ganic receptors. The combination of systemic elements into 
actual experiences is similar to the process by which external 
sensations combine to form perceptions. But the distinction 
between perceptions and feelings is more than a difference in 
the sort of receptors which furnish the material. The qual- 
ities of the elementary constituents are subject to different 
kinds of alterations in the grouping. 

In perception the specific qualities of the sensations be- 
come more vivid in the grouping. Some of the constituents 
are more definitely marked off and discriminated; others 
fuse together and the resulting state takes on a new quality 
which is specific and distinct. On the other hand when sys- 
temic sensations unite to form a feeling, the specific qualities 
of the components become less distinct; they merge into the 
general hedonic quality of pleasantness or unpleasantness. 

Compare the following experiences: (1) The sight of some 
painting, such as " Signing the Declaration of Independence." 
(2) The sound of the final chord of music in an orchestral 
piece. (3) The agony of an intense toothache or burn or 
bruise. (4) The pleasant languor accompanying the diges- 
tion of a hearty meal. 

The first two examples are perceptions. Here the specific 
qualities are prominent. In the painting the several human 

^ The term feeling is often applied to any indistinct sensation. This is an 
older use. The use ol feeling to denote sensations of touch ("to feel the tex- 
ture of cloth") is likely to cause confusion and should be avoided in psy- 
chology. Hedonic is used as an adjective for feeling ; hedonic experience, 
hedonic quality, etc., mean 'feeling experience,' 'feeling quality,' etc. Affec- 
tion and affective state may be used interchangeably with feeling. 



280 FEELINGS 

figures stand out, they are discriminated and localized in 
space relations. In the musical chord the tone-pattern of 
the clang is distinct, despite the fusion of the components. 

The last two examples are feelings. In the pain experience 
the quality of unpleasantness dominates over the specific 
quality of the receptor — whether tooth or skin or muscle. 
In the languor experience the specific quality arising from 
the receptors in the digestive organs is scarcely observed; 
the general hedonic quality of comfort (pleasantness) pre- 
dominates. 

This predominence of the general hedonic quality over the 
specific qualities of the components increases as the number 
of constituent elements becomes greater. We localize a 
pin-prick quite definitely, and the pricking quality is fairly 
distinct. But if a great number of receptors are affected the 
localization becomes more vague and the specific quality 
grows indistinct. One is not always certain whether a cer- 
tain pain is merely toothache, or toothache and earache com- 
bined. It is localized now in one part of the head, now in 
another. The same is true of digestive pains. In general, 
the more pervasive the feeling, the less clear and distinct are 
its specific component qualities and the more dominant the 
general hedonic quality. 

Systemic components usually enter into our perceptions. 
For this reason some writers regard hedonic tone as a char- 
acter or attribute of sensation, ranking it along with quality 
and intensity. From this point of view feeling is not a 
sensation, but a factor in the make-up of sensations. 

If we observe our own experiences derived from the ex- 
ternal senses we do find an hedonic quality attaching to 
many of them. The pleasantness of an harmonious chord and 
the unpleasantness of a noxious odor are elements in these 
perceptions. It is doubtful, however, whether the hedonic 
tone is a character of external sensations. It is more probably 
an added component, like the taste of the uncut orange. This 



NATURE OF FEELING 281 

is supported by the fact that we learn to ' Hke ' certain odors 
which were once unpleasant and to ' dislike ' tones or colors 
which were formerly pleasing. On the other hand the gen- 
eral hedonic tone of organic and pain experiences is closely 
bound up with the specific stimuli of these senses. It changes 
only as these stimuli alter or as other systemic stimuli occur 
to modify the general central effect. 

The physiological processes and the data observed in sub- 
jective experience seem best explained if we regard both the 
specific organic and pain qualities and the hedonic tone as 
due to interoceptive activity. The feeling tone which ac- 
companies sight, hearing, etc., is due to a simultaneous stim- 
ulation of some internal receptors. Close observation indi- 
cates that organic sensations accompany the perception in 
all such cases. Extreme instances of this are the " ebullition 
of feeling " attending a full rich chord in music or the nausea 
aroused by a rank odor. 

Characters of Feeling. — The characters or attributes 
which appear in perceptions are found also in feelings. Quality 
and intensity are the most important characters of feeling 
states. Duration varies with the duration of the stimulus. 
The extensity character is vague and indefinite. We dis- 
tinguish between a pervasive pain or organic feeling, and 
a localized feeling; but the localization and extent of a perva- 
sive feeling are not clearly defined — feelings derived from 
a group of receptors are not definitely related in a spatial 
manner to other feelings or to our perceptions. The grouping 
process is accompanied by a certain amount of focalization, 
which introduces the character of vividness. 

The qualities of feeling, as already stated, include two 
independent variables, a general hedonic quality, or feeling- 
tone, and a specific quality which depends upon the nature 
of the stimulus and receptor. Of these, the hedonic tone is 
more prominent. There are two qualities of hedonic tone: 
pleasantness and unpleasantness. 



282 FEELINGS 

Certain writers have claimed that other hedonic quahties 
exist. Thus Wundt finds three pairs of opposite quahties: 
pleasantness and unpleasantness, excitement and quiescence, 
strain and relief. Strain and relief are probably due to 
kinesthetic components which accompany certain feelings. 
Excitement and quiescence are due in part to the intensity 
factor and partly to kinesthetic stimuli; they characterize 
emotional states rather than feelings. 

The intensity of pure feeling states is difficult to measure. 
Some attempts have been made, however, to measure the 
intensity of the hedonic tone of perceptual states. When the 
intensity of an external stimulus is increased continuously 
the intensity of the accompanying feeling varies also. But 
the change does not follow Weber's Law. We are dealing 
with a phenomenon which has two opposite phases, pleasant- 
ness and unpleasantness. 

The general relations between intensity of external stimu- 
lation and hedonic intensity may be stated as follows : 

(1) With a minimal intensity of stimulation the hedonic 
accompaniment is zero. 

(2) As the intensity of the stimulus increases there is at 
first a slight degree of pleasantness. 

(3) With further increase in intensity of stimulation the 
pleasantness increases to a maximum and then decreases. 

(4) At a certain point the pleasantness disappears entirely, 

(5) With further increase in intensity of stimulation un- 
pleasantness appears and from this point on increases steadily. 

(6) With great intensity of stimulation a maximum degree 
of unpleasantness occurs; this marks the beginning of actual 
destruction of some of the tissues. [Fig. 68.] 

Focalization occurs in the formation of feelings, though 
not so effectively as in perception. This central process 
furnishes the character of vividness. Many separate systemic 
sensations may be stimulated at the same time. Where all 
bear the same hedonic tone, they sum up into one general feel- 



CHARACTERS OF FEELING 



283 



ing experience, pleasant or unpleasant. Where they differ 
in tone, one feeling or group of feelings is focalized and the 
rest become marginal. An illustration of the combination 
effect is observed when a pleasant day, good news, and a 
well-ordered digestion combine to make us thrill with the 




— ar' 



Fig. 68. — Hedonic Curve 

Dotted curve shows change in degree of pleasantness (above x 
axis) and unpleasantness (below x axis) with increase of stimulus 
(left to right along x axis). The corresponding changes in intensity 
of pressure sensation are shown by the unbroken curve. [From 
Pillsbury, after Wundt.] 



joy of living. The conflict is illustrated by the feeling of a 
wounded soldier who is oblivious to intense pain in the exul- 
tation of victory. 

In general our mental life at any moment is characterized 
by a pervasive feeling state of some sort. Specific external 
experiences or ideas modify this general feeling tone from 
time to time, but we rarely find in the focus of conscious ex- 
perience two conflicting feelings. Some writers in fact have 
declared that pleasantness and unpleasantness cannot be 
experienced together at the same time. This is one of those 
dogmatic generalizations which the scientist usually finds 
reason to challenge. 



284 FEELINGS 

Under exceptional conditions it is certainly possible to 
experience two conflicting feelings. We experience pleasure 
when a friend sympathizes with us on the agony of an ex- 
cruciating toothache; but this does not altogether obliterate 
the discomfort of the ache. At such times we experience 
both the unpleasant and the pleasant simultaneously, and it 
may be with equal vividness. 

Appetite and Aversion ; Excitement. — The consolidation 
of systemic sensations into states of feeling is far less de- 
veloped in man than the consolidation of external sensations 
into perceptions or of ideas into imagery. There are several 
reasons for this. The systemic sensations are not qualita- 
tively differentiated to the same extent as sight, hearing, 
touch, or smell. They are produced (except in the case of 
pain) by internal stimuli which are constantly changing. 
They are less closely connected with environmental condi- 
tions, which are of supreme importance in the life of the 
organism. 

In civilized man systemic sensations are more frequently 
experienced as components of perceptions, imagery, and other 
states, than as independent states of feeling. At times, how- 
ever, the intensity of the organic or pain stimuli is so great 
that the mental state is predominantly one of feeling, with 
the other components subordinate. These definite states of 
feeling may be divided into two classes, appetites and aver- 
sions, according as the dominant hedonic quality is pleasant 
or unpleasant. 

Feelings of appetite result most frequently from digestive 
and sex sensations, while feelings of aversion are due to pain 
sensations and sensations arising from disturbed digestive 
conditions. In many cases the hedonic tone of a feeling is 
not pure. The feeling of digestive appetite, for instance, 
includes hunger components whose tone is unpleasant. A 
pain may be accompanied by pleasant sensations due to the 
healing process. At times the hedonic tone is indefinite, as 



APPETITE AND AVERSION; EXCITEMENT 285 

in cases of excitement. Intense feelings of any sort are apt to 
be accompanied by very intense kinesthetic components and 
are thereby transformed into emotions.^ 

Role of Feeling in Mental Life. — The importance of feel- 
ing in mental life is apt to be overlooked, owing to the empha- 
sis usually laid upon perception and imagery. The external 
senses and their imagery give information concerning the 
world about us. In the same way the systemic senses give 
us indications of our own physiological condition. These 
data are consolidated into feelings. 

The influence of feeling in determining our attitude to- 
ward the outer world may be observed by comparing the 
responses of different individuals under similar conditions; 
or better stUl by observing how differently the same individ- 
ual acts in two cases where the external situation is similar 
but his own internal condition is radically different. 

Some men apparently can never be disheartened or insulted; 
others wiU collapse at the slightest misfortune, or bristle at 
the most trivial remark. The external stimuli are alike; the 
difference lies in their systemic condition. The same man 
who meets difficulties energetically and cheerfully when in 
good health, may sit despondent and refuse to face danger 
or perplexity when affected by indigestion, malaria, or other 
weakening influences. 

The real significance of feeling in our mental life can only 
be understood through a study of its biological history. 
Destruction of tissue is harmful to any creature. Hence, any 
creature which develops a means of avoiding such destruction 
will stand a better chance of surviving. Those creatures 
which are able (1) to avoid noxious stimuli and (2) to react 
positively to beneficial stimuli are more likely to survive in 
the long run. The mechanism for each of these two opposite 
types of response is developed through one of the phases of 
feeling. 

^ See ch. xiv. 



286 FEELINGS 

The external receptors are not harmed except by very 
intense stimuli: hence, the pain nerves furnish an adequate 
means for discriminating harmful external stimuli from those 
which are beneficial or neutral. The internal organs require 
more delicate indications. They are more liable to dis- 
organization through fatigue, poison, and other detrimental 
influences. But they do not ordinarily require a fine dis- 
crimination of qualitative influences. Hence, instead oi 
building up complex ' perceptual ' relations and qualitative 
distinctions like the external senses, the organic senses have 
developed central connections whereby their data tend to 
fuse into mass experiences — they furnish us indications of 
general pleasantness or comfort and of general unpleasant- 
ness or discomfort. 

Mental life is above aU concerned with the interaction be- 
tween the organism and its environment. , Accordingly, the 
most important development of the feeling experience is 
found in its combination with kinefsthetic experiences to form 
emotions, which generally involve reaction upon the outer 
world. 

4. Conations (Expressive States) 

Nature of Conative States. — Every nerve impulse tends 
to discharge sooner or later into a motor nerve path. This 
motor discharge either produces muscular contraction; or it 
excites activity of the glands, which results in secretion. In 
either case the first effect of the motor discharge is to produce 
some motor activity which may serve as stimulus to a new 
sensory impulse. The resulting sensation ' reports ' the result 
of the motor discharge. 

In the case of glandular activity the report is indirect. So 
far as we know the glands are not provided with special re- 
ceptors; but the secretory activity may stimulate some of 
the external or internal receptors. A tragic story may start 
a motor impulse to the tear glands, resulting in the shedding 



NATURE OF CONATIVE STATES 287 

of tears. Even apart from muscular accompaniments (such 
as sobbing), the flow of tears on the eyeball or down the 
cheeks serves as a stimulus to sight and touch. In the same 
way the sight of a juicy peach starts a motor impulse to the 
salivary glands; the mouth ' waters ' and this moisture serves 
to arouse sensations of taste and touch. 

When the motor impulse affects the muscles the sensory 
effect is more direct. Muscular contraction and the resulting 
bodily movements are reported at once by stimulation of 
receptors situated in the muscles themselves. These stimuli 
and sensory impulses result in kinesthetic sensations (ch. x). 
Kinesthetic sensations combine together in the same way 
as external sensations or systemic sensations. Mental states 
in which kinesthetic components predominate are called 
expressive states or motor consciousness ; a convenient term 
is conation. 

Until recently it was supposed that we are directly aware 
of the outgoing motor impulse. Many observations and 
experiments, however, have shown quite conclusively that 
motor experiences are due wholly to sensory processes stim- 
ulated by the muscles, tendons, and joints as they move or 
are maintained in a fixed position. Conation, or motor con- 
sciousness, is our experience of the condition of our muscles 
and other motor organs or of the changes which they undergo 
in actual movement. It is a report from the organs to the 
center, not an experience of sending out motor impulses from 
the center. 

Conation and Volition. — In examining behavior from the 
standpoint of the outside observer (ch. vi, vii), we distin- 
guished between two types of complex behavior: instinct and 
intelligence. The mechanism for instinctive behavior is 
inherited. The structure used in intelligent behavior is 
largely inherited also, but the central connections are man- 
ifold, and individual experience determines which one of 
several possible paths is actually joined up in any instance. 



288 CONATIONS 

When we observe our own motor experiences the dividing 
line is somewhat different. Instinctive acts and habitual 
intelligent acts are performed without hesitation. Sensa- 
tions of various sorts find immediate expression and are fol- 
lowed at once by conative mental states. In neural terms 
this means that the sensory impulses are integrated and pass 
over without delay into motor paths, causing coordinated 
movements, which immediately stimulate kinesthetic (and 
sometimes static) sensory impulses. This type of activity 
is usually called sensorimotor. 

Distinguished from this ' automatic ' activity we find an- 
other type of intelligent behavior in which the motor discharge 
is delayed while new connections are formed at the centers. 
Sensations are followed by ideas and the motor discharge 
does not occur till later. In these experiences, images or 
thoughts are interpolated between the original sensations and 
the conative states. In neural terms this means that a 
longer central arc is involved, and that the central impulse 
is modified by the retention traces in these interpolated 
central neurons. This type is called ideomotor activity. 

A mental state which occurs as the result of sensorimotor 
activity is a simple motor experience or conation. We may 
define conation as the mental state which accompanies 
any ' involuntary ' or ' automatic ' movement or any bodily 
position of which we are aware. When we dodge to avoid 
being hit, or when we adjust our steps In walking, our ex- 
perience of the action is a conation.^ 

In ideomotor activity the mental state includes not only 
kinesthetic sensations, but also an image of some sort which 
pictures the performance of the movement. This type of 

^ If the motor activity is entirely unobserved, as happens in certain cases 
of extreme inattention, it is scarcely proper to class it as 'mental state' at 
all. We find om-selves at a certain gate without any recollection of our move- 
ments in getting there. These extreme automatic movements may be ex- 
perienced in some detached system of arcs, but of this there is no certainty. 



CONATION AND VOLITION 289 

mental state is called volition. Volition involves two kinds 
of components, external ideas and motor sensations.^ 

Composition of Conative States. — Our conative mental 
states are combinations of various elementary data in which 
kinesthetic and static sensations predominate; they include 
also elementary kinesthetic ideas and certain data from sight, 
touch, etc., which indicate the position and movements of 
our body or some of its members. By discriminative ob- 
servation we can distinguish sensations of pull, strain, force, 
energy, effort. When the movement is checked by some 
obstacle or impeded by an opposing force we have a sen- 
sation of expended energy, or resistance. 

This ' dynamic sensation ' is the specific quality of conative 
states. It does not imply actual performance of movement 
or ability to perform it. If a muscle has been injured or the 
nerve leading to it is severed we may nevertheless experience 
the sensation of power or energy. Where a muscle and its 
motor pathway are unimpaired but we have not learned to 
connect them up, we may still experience the sensation of 
effort. In such cases careful observation shows that the 
sensation is due to slight motor stimuli in the neighborhood 
of the muscles in question. Although we do not actually 
contract the ear muscles, we do send motor impulses to other 
muscles in the same general region; in the case of injured 
muscles or severed nerves the kinesthetic sensations are real, 
but they come from neighboring muscles. 

The imagery factors included in conative states are mainly 
reproductions of external sensations. We recall the position 
of our arm, head, or other member as seen or ' palped.' 
Muscle-sense imagery is vague and enters into the exper- 
ience but slightly: the kinesthetic image tends to produce an 
actual movement, so that usually actual kinesthetic sensa- 
tions predominate over the corresponding imagery. 

Hedonic elements, especially pain, enter prominently into 
^ Mental states with a two-fold basis will be treated in the next two chapters. 



290 CONATIONS 

some conative states. These feeling components often ini* 
tiate secondary motor impulses which tend to inhibit certain 
movements and reinforce others. The perception of a flame 
may lead to a withdrawing movement and the perception of 
a luscious peach may bring about a grasping movement. The 
motor impulse is initiated in one case by the unpleasantness, 
in the other by the pleasantness of earlier experiences. 

Conations or simple motor states of consciousness, then, 
consist essentially of kinesthetic and static sensations, to 
which are added auxiliary elements from the external senses, 
together with memories and hedonic elements. Conation is 
generally not so vivid as perception, but it constitutes a well- 
organized experience; this organization shows itself in the fine 
motor adjustments which take place in sensorimotor activity. 

Varieties and Role of Conation. — Conative states are 
classified according to the type of behavior which they 
accompany. Human conations include the following classes; 

Reflex conations > 

Instinctive conations 
Tendential conations 
Habit conations 

Reflex conations occur when a reflex action generates a kin- 
esthetic stimulus, whose impulse reaches the higher centers. 
When we start at a sudden noise the movement resulting 
from the reflex arouses a conative mental state. Coughing 
and sneezing are accompanied by conation. If we test the 
various reflexes listed in Table III (p. 101), we find that in 
nearly all cases the activity is accompanied or immediately 
followed by motor sensations which are grouped together 
into an integrated mental state — a motor experience or 
conation. In some reflexes the secondary motor sensations ^ 
are most prominent; — in winking we experience especially 
the visual change, in sobbing and laughing the auditory 
sensation. In other reflexes the kinesthesis is subordinated 

1 See p. 210. 



VARIETIES AND ROLE OF CONATION 291 

to perception or feeling; iris and accommodation sensations 
enter into perceptual states and lose their identity; they make 
for 'clearer vision.' 

Instinctive conations most frequently accompany instincts 
classed as nutritive (Table IV), such as wandering, acquiring, 
cleanliness. In mental states which accompany other types 
of instinct the systemic components are apt to be more vivid; 
in fighting, sympathizing, mating, and even in modesty re- 
actions, the mental state is an emotion. 

The states which characterize instinctive tendencies are 
sometimes emotional, sometimes volitional, but in many 
cases they are dominantly conative in type. These states 
may be called tendential conations. There are many in- 
stances of sensorimotor curiosity in which the mental state 
is almost wholly conative, with only marginal elements of 
feeling or imagery. 

Imitation, when it occurs spontaneously, is a typical cona- 
tive experience. It depends upon inherited mechanisms 
which connect external receptors with motor paths leading 
to muscles in the appropriate regions. When we see another 
person perform a certain movement with his hands, the motor 
paths to our own hand muscles may receive an impulse; when 
we hear a succession of musical sounds the motor paths to 
our vocal muscles are likely to be excited. The mental state 
in such cases is a conation. 

Conative mental states accompany intelligent acts when 
these proceed without delay and without the intercalation of 
higher central neurons in the arc. Our fixed habits belong 
to this class. The mental states which accompany them 
may be called habit conations. When one signs his own name 
the mental state which accompanies the neural response in 
most cases is essentially conative. Singing, piano-playing, 
recitation, typewriting — all such learned acts may be non- 
voluntary, and the corresponding experiences are conative. 

At times such acts are performed with only marginal con- 



292 CONATIONS 

sciousness, but usually some focalization is essential. If the 
focus of consciousness is elsewhere the act miscarries, and we 
make some absurd blunder. We tear up the letter instead 
of the envelope; or we summon the maid and when she comes 
we have no idea what we wanted. Fixed habits in general 
are sensorimotor (not ideomotor) and are centrally character- 
ized by conation. 

Conative mental states do not occur so frequently in the 
aggregate as the other primary states. Vivid imagery or 
vivid feeling usually accompanies the kinesthetic elementSj 
so that the resulting experience contains two kinds of com- 
ponents and becomes a secondary state; it is a volition if the 
ideational factor is prominent, an emotion if the systemic 
factor is strong. In human mental life conation generally 
rises into voluntary activity. In subhuman species the more 
prevalent type is emotion. 

Collateral Reading: 
Titchener, E. B., Text-Book of Psychology, sees. 68-74, 112-126. 
James, W., Psychology, chs. 18, 19, 23; Principles of Psychology, ch. 18. 
Angell, J. R., Psychology, chs. 8, 9, 13, 14. 
Kiilpe, O., Outline of Psychology (trans.). Part I, sec. 2. 
Pillsbury, W. B., Fundamentals of Psychology, chs. 6, 10, 13. 
Breese, B. B., Psychology, chs. 10, 11, 16. 

Judd, C. H., Psychology, General Introduction (2d ed.), chs, 9, 11. 
Royce, J., Outlines of Psychology, ch. 7. 

Galton, F., Inquiries into Human Faculty, ch. on Mental Imagery. 
Hering, E., Memory (trans.). 

Washburn, M. F., Movement and Mental Imagery, chs. 1-5. 
Peillaube, E., Les images. Part I. 

Titchener, E. B., Psychology of Feeling and Attention, chs. 2-4. 
Miinsterberg, H„ Die Willenshandlung. 

Practical Exercises: 

Read a chapter from some history or novel, and note the images which 

are aroused; classify them according to image-type and sense-type. 
Lying in bed at night with closed eyes, try to picture imaginary scenes or 

stories. Describe the experiences; compare their vividness with real 

scenes; how far are they due to retinal stimulation.? 
Analyze your general state of feeling at three different times; e.g., on wak^ 

ing, after a hearty meal, after a brisk walk. 
Analyze the experience of catching a ball. 



CHAPTER XIV 

SECONDARY MENTAL STATES 

Nature and Classification of Secondary States. — In the 
two preceding chapters we have examined the mental states 
which are homogeneous — whose chief components all belong 
to the same general class. There are in addition certain 
kinds of mental states into which two or more varieties of 
data enter. Thus emotion is a mental state which combines 
systemic and motor elements. An emotional state is usually 
aroused by some external stimulus or by some ideational 
state, but in the emotional experience itself the perceptual 
or imagery components are subordinate elements. For ex- 
ample, an emotional state akin to our experience of anger is 
aroused in a bull when he sees a red cloth; the red percep- 
tion is the basis of the emotion, but the emotional state is 
systemic and kinesthetic. In man, the emotion of love may 
be aroused by the sight of a fellow-being or the sound of a 
well-modulated voice; but the emotion itself is a combination 
of feeling and conation. For want of a better term these 
heterogeneous mental states will be called secondary, though 
some of them may have originated prior to primary states, 
and they are frequently less complex than the latter. 

Data from the external senses (perceptual elements) are 
rarely if ever among the prominent constituents of secondary 
states. External stimuli are so intense and obtrusive that 
the resulting impulses either reduce the other constituents to 
a subordinate role or else they themselves become sub- 
ordinate through focalization of the other elements. In 
anger the systemic and motor sensations, once aroused, tend 
to become exceedingly vivid, and the perception which aroused 
them becomes marginal. But if we focus the perception — 
if we attend to the external situation — the emotional state 



294 SECONDARY MENTAL STATES 

fades into the background, and we cease to be angry. In 
secondary states ideational elements take the place of ex- 
teroceptive data. 

There are well-defined classes of secondary states for each 
pair of components, excluding external sensations; and there 
are states into which all three sorts of components enter as 
focal constituents. The classes of secondary states are shown 
in Table XV. It will be noticed that in certain cases there 
is more than one line of development. Volition, thought, and 
language are various types in which ideational and kines- 
thetic components are dominant, Language differs from 
volition in the prominent part which the social factor plays 
in its development. 

Table XV. — Secondary Mental States 
Mental States Dominating Components 

Emotions Systemic and Motor Sensations 

Sentiments Ideas and Systemic Sensations 

Volitions Ideas and Motor Sensations 

Thought and Language (Social) . . . Ideas and Motor Sensations 

Ideals and Rational Actions (Social) Ideas; Systemic and Motor Sensations 

1. Emotions 

Nature of Emotion. — An emotional state is a combination 
of systemic and motor elements. It is characterized by a 
vivid feeling tone, either pleasantness or unpleasantness; 
and a specific systemic quality is usually prominent, due to 
the condition of certain internal organs, or to the mode of the 
pain stimuli if these are concerned. In emotion there is also 
great muscular activity or a condition of high muscular 
tension. These kinesthetic stimuli excite motor sensations, 
which are always a prominent factor in the emotional ex- 
perience. 

Emotion is the earliest secondary state to arise in the 
animal series. The fundamental emotions of fear, anger, 
and love appear well down in the biological scale. It should 



NATURE OF EMOTION 295 

be noted too that emotion is the only secondary state in 
which ideational elements do not play a prominent part. The 
experience is aroused by external stimuli or ideational im- 
pulses, but in the emotional state itself these components are 
unimportant. Emotion is concerned far more with our bodily 
organization and with action upon the environment than 
with perceptions or ideas of the outer world. 

According to the older psychology, feeling constitutes the 
chief factor in emotion: the systemic sensations were sup- 
posed to occur before the kinesthetic and to furnish the 
stimulus for the motor phenomena. This interpretation 
assumes that we first experience the feeling of anger, then 
clench our teeth and fists, scowl, and assume the general an- 
ger attitude. William James and Carl Lange independently 
suggested that the factors really arise in the opposite order:/ 
We first of all assume the anger attitude — clench our teeth 
and fists, and strain the tension of our muscles; these move- 
ments stimulate in turn the anger feeling. That is, accord- 
ing to these writers, the motor components generate the feeling 
components of the experience. 

Some confirmation of this theory is found in the fact that 
if we artificially assume the anger attitude with all its kin- 
esthetic accompaniments, the feeling elements are thereby 
aroused to a noticeable degree; on the other hand in natural 
anger, if we succeed in relaxing the muscles and thus rid 
ourselves of the kinesthetic elements, the feeling of anger 
diminishes and the entire emotion tends to vanish. 
/On the whole, however, the facts seem to indicate that the 
systemic and kinesthetic factors are coordinate; both are 
aroused by some perceptual or ideational experience — both 
arise simultaneously. If we succeed in relaxing the muscles, 
the emotion vanishes — it passes over into a simple state of 
feeling. If we succeed in removing the systemic components 
the experience reduces to mere conation. Most persons are 
able to control their motor expressions more readily than their 



296 EMOTIONS 

systemic processes. Hence, when we make an experimental 
test the kinesthetic factor seems to be the crucial factor. In 
point of fact, emotion is the joint product of systemic and 
kinesthetic impulses. 

Primitive Types of Emotion. — Emotion is the most prim- 
itive of all the secondary mental states. We gain consider- 
able insight into its nature by studying its manifestations 
in various animal species. But this study has consisted too 
frequently in reading human emotions into animals, just as 
popular psychology is apt to read too much of human thought 
and reasoning into subhuman types of behavior. 

A better insight is gained by reading animal experiences 
into man. When a cat marches majestically away from a 
growling dog with an air of offended dignity, we are naturally 
inclined to read into her experience the ideas and thoughts 
which cause the corresponding display in man. But it is 
more profitable psychology if we realize that the inciting 
stimulus in the animal is purely perceptual. From the sim- 
ilarity of the behavior manifestation in the two cases we 
may reasonably infer that even in man the pride emotion is 
due more to perception and less to ideas than is generally 
supposed. 

The analogy should not be pressed too far. In point of 
fac> human emotion differs from animal emotion chiefly in 
the prominent part played by imagery and other ideational 
experiences in its production. Few of our emotions in adult 
life are purely perceptual, like the anger of the bull at the 
sight of red. A child cries when we pinch a rubber stopper, 
or manifests fear at the sight of a snake or some other strange 
creature. In the adult, emotions are determined by ideas 
rather than perceptions. We are angry when we see a big 
boy beating a small boy; we are not angry when we see a 
strong man beat a rug. 

The most primitive emotions in man are those whose 
bases are found in long inherited structure, and which may 



PRIMITIVE TYPES OF EMOTION 297 

be traced far down in the animal scale. The three most 
fundamental types are anger, fear, and love. 

The hedonic tone of fear is unpleasantness, which is usually 
present in a hig^ degree of intensity. The specific organic 
sensations which occur in fear are stimulated through re- 
ceptors in the lower viscera and in the region of the lungs 
and heart. The characteristic motor phenomena of fear are 
certain definite muscular contractions, which produce trem- 
bling, shrinking movements, raising of the eyebrows, etc. 
These motor activities furnish kinesthetic sensations which 
enter prominently into the emotional experience. 

In anger the general hedonic tone is characteristically un- 
pleasant, but it is not so prominent as in fear. The specific 
systemic sensations are connected with the upper digestive 
tract, the heart and lungs, and the circulatory system gen- 
erally. An outburst of anger is accompanied by vigorous 
heart activity and breathing, which usually causes intense 
flushing of the face and sometimes a choking sensation and 
suffusion of the eyes. The characteristic motor activities 
are clenching of the fists and teeth, strained tension of the 
facial muscles, and rigidity of the lower limbs. These motor 
activities are accompanied by very intense kinesthetic sensa- 
tions. The expression of anger is generally movement toward 
the object — in fear the movement is away from its object. 

Love is the third type of primitive emotion. Its char- 
acteristic feeling tone is pleasantness.^ The specific systemic 
qualities are less prominent than in fear or anger; they arise 
from the region of the lungs and from the sexual organs. The 
popular notion which associates the emotion of love with the 
heart is not so far wrong: careful observation shows that 
the sensation is located somewhat above the heart, but that it 
is due to the circulation and not to breathing. There are 
various motor accompaniments of this emotion, and the 
kinesthetic sensations which these excite enter prominently 
into the experience. A somewhat less intensive variety of 



298 EMOTIONS 

the emotion is found in sympathy. Here the hedonic tone 
(pleasantness) is predominant, and the specific qualities are 
less definite than in love. The motor tendencies in sympathy 
are generally ' movement toward ' the object, and are often 
accompanied by activity of the tear glands. 

Classification of Human Emotions. — The emotions ob- 
served in man have been classified in various ways according 
as one characteristic or another is the fundamental criterion. 
They may be grouped according to their temporal reference 
(present, past, or future), their object (emotions regarding 
ourselves, our fellow men, animals, and inanimate objects), 
hedonic tone (pleasant or unpleasant), or rate of increase 
(abrupt or gradual rise). All these conditions are important 
factors, but they do not indicate the relative importance of 
the several kinds of emotions. Some types of emotion have 
developed tremendously; others which parallel them are 
quite trivial. A purely logical scheme fails to bring this out. 
We can only determine by actual observation and exper- 
iment just what emotions actually play an important r61e in 
life. 

Since the emotional life dates far back in organic history, 
we can utilize subhuman material to a greater extent than in 
other mental states. But this applies only to emotions which 
refer to the present: retrospective and prospective emotions 
are founded on vivid memories or vivid anticipation images 
which do not occur in subhuman species. Al\ important aid 
in the study of emotions is the names of emotional states 
found in the languages of civilized and uncivilized races. 
Experiences which reach further back in race history are 
likely to be named first and to have a greater variety of 
differential names than those recently acquired. 

W. McDougall has pointed out that many emotions cor- 
respond more or less exactly to types of instinctive behavior. 
But human instincts, as we found in chapter vi, have be- 
come modified in various ways by intelligence; certain emo- 



CLASSIFICATION OF HUMAN EMOTIONS 299 

tions have been inhibited or strengthened so that the parallel 
with instinct is obscure. In some cases two or more types 
of emotion correspond to the same instinct, A list of the 
more important human emotions with their instinctive bases 
is given in Table XVI. [Cf . Tables IV and V.] 



Table XVI, — Human Emotions 



1. Expressive {Nutrit 


ive) » 


2. Reproductive 




Emotion 


Basis 


Emotion 


Instinct 


+ Joy (Enthusiasm) 


Diffused feeling 


+ Love 


Mating 


— Grief (Despair) 


" 


+ Lust 


" 


- Shock 


" 


— Jealousy 


" 


+Mirth 


« 


— Coyness 


" (female) 


+ Ecstasy 


« 


+ Tenderness 


Maternal 


Restiveness 


" 






Exuberance 


Play 






+ Wonder 


Curiosity 






3. Defensive 




4. Aggressive 




Emotion 


Instinct 


Emotion 


Instinct 


— Fear 


Flight and Hiding 


— Anger (Passion 


) Fighting 


— Disgust 


Avoiding 


- Hatred 


Resenting 


- Timidity 


Shyness 


— Envy 


Rivalry 


(Embarrassment) 




+ Pride 


Domineering 


— Shame 


Covering 


+ Exultation 


" 


+ Awe 


Subjection 






5. Social 




6. With Temporal Projection 


Emotion 


Instinct 


Retrospective Reference: 


+ Affection 


Family 


— Regret (Remorse) 


+ Cordiality 


Gregarious 


+ Satisfaction (Elation) 


-Pity_ 


Sympathetic 


Surprise 




+ Gratitude 


" 


Prospective Reference: 


+ Admiration 


" 


+ Hope 




— Detestation 


Antipathetic 


— Dread 




— Revenge 


" 


Anxiety 




— Suspicion 


« 






— Scorn 


" 







There appear to be no specific emotions directly attached 
to the nutritive instincts. There are, however, a number of 



300 EMOTIONS 

' expressive ' emotions, such as joy and grief, which are prob- 
ably indirectly due to the nutritive functions. On the other 
hand the expressive emotions of exuberance and wonder are 
not traceable to the nutritive functions at all, but to the 
instinctive tendencies of play and curiosity. There appears 
to be a fairly close correspondence between the remaining 
types of instinct (reproductive, defensive, etc.) and well- 
marked types of emotional experience. Certain additional 
emotions are differentiated on the basis of their temporal 
projection. The prospective emotion of hope, and the retro- 
spective emotion of satisfaction are similar to joy apart from 
the temporal coefficient. These types make up a sixth class, 
which has apparently no instinctive basis. 

In many cases we may readily note a number of different 
shades of emotion which belong to the same general type. 
Some of these varieties are of considerable importance in 
mental life and have received distinctive names. Remorse, 
for example, plays quite a different role in mental life from 
regret. Only the most prominent variations are given in the 
Table. 

The hedonic tone of the emotions is indicated in the Table 
by + where the tone is pleasant, and by — where it is char- 
acteristically unpleasant. The emotions of uncertainty 
(restiveness, surprise, anxiety) may be characterized by 
either tone; frequently the tone alternates between one 
quality and the other. ^ 

, Role of Emotion in Mental Life. — The emotions, more 
than any other kind of mental states, represent by-gone con- 
ditions of life. Many of them may be regarded as fossil 
remains of our prehuman ancestors. They do not fit par- 
ticularly well into the human world of to-day. This is 
apparent in the efforts which the community makes, through 
tradition and schooling and family training, to suppress or 

^ Tor treatment of the motor manifestations of emotion see references at 
end of this chapter, especially Cannon and Crile. 



ROLE OF EMOTION IN MENTAL LIFE 301 

modify their manifestation. These attempts to reduce our 
emotional life to a minimum are not always well advised. 
Suppression is not necessarily eradication. Freud has shown 
that the ejEIort to repress often results in nervous disorgani- 
zation. On the moral side it fosters deceit and hypocrisy. 

The objection to the contemporary attitude toward emo- 
tion is that it is not founded upon psychological analysis. If 
we study the emotions separately we find that they differ 
considerably in value. Some are distinctly harmful to the 
individual in his relations to the environment — especially 
the social environment. But others are quite as truly 
beneficial, while others may be classed as neutral. 

There is no doubt that the defensive emotions refer back 
to prehistoric modes of defense, and that for the most part 
they hamper us under modern conditions. This is even 
more true of aggressive emotions. On the other hand the 
social emotions harmonize well with modern social conditions, 
except those based upon the antipathetic instincts. The 
reproductive emotions require training to fit them into the 
social life of to-day; but in some communities this training 
has gone to extreme lengths. The reproductive instincts are 
fundamental to life ; we may tone down their primitive modes 
of expression, but in suitable form they are a requisite part 
of the individual's mental life. , 

In general, the expressive emotions and the corresponding 
retrospective and prospective types may be classed as neutral 
from the social standpoint. In their extreme manifestations 
they do not fit in with modern life. But a moderate display 
of joy, grief, mirth, regret, hope, and the like is not socially 
detrimental and is of some benefit to the vital life of the 
individual. 

What has just been said is not intended as a lesson in ped- 
agogy, though it might well be taken into account in our 
program of self-training. It is merely to point out that the 
emotional part of our mental life is to some extent an an- 



302 ' EMOTIONS 

achronism. Emotion, if uncontrolled, hampers the proper in- 
terrelation between the individual of to-day and the environ- 
ment of to-day. It is only when the instinctive emotions are 
trained into intelligent modes of expression that this phase of 
mental life works harmoniously with the rest. /^ 

2. Sentiments 

Nature and Classes of Sentiment. — A sentiment is a 
mental state whose leading components are feelings and im- 
agery. It is due to the combination of systemic with idea- 
tional impulses.^ 

Sentiments may be aroused by any sensory or ideational 
impulse, but the state aroused is essentially different from 
a perception or an image. A typical example is our " sense 
of beauty," which is not a sensation nor a perception, but a 
sentiment. The experience may be brought about by seeing 
the Venus de Milo or by listening to Beethoven's Fifth Sym- 
phony; or the memory of one of these may arouse the same 
experience. The sentiment of beauty, however, is distinct 
from the perception or other state which arouses it. The 
perception suggests the sentiment; a radical transformation 
of the mental states takes place, and the sensory and other 
components of the antecedent state drop out or become sub- 
ordinated. The focal components of a sentiment include ele- 
ments of two sorts : an idea of value ^ and a feeling. 

Sentiments are classed according to the type of primary 
experience which arouses them. The principal varieties of 
sentiment and the states which suggest them are shown in 
Table XVII. 

^ The term sentiment has a somewhat technical meaning in psychology. 
It is not precisely what we mean by ' a sentiment ' in ordinary language, nor 
does it correspond to the adjective 'sentimental'; but it carries a trace 
of each notion — the imagery of the former and the feeling tone of the 
latter. 

^ For the discussion of value, see ch. xv. 



NATURE AND CLASSES OF SENTIMENT 303 

Table XVII. Classification of Sentiments 
Sentiments Source 

Reality Feelings Perceptions 

Beliefs Ideational States 

Esthetic Sentiments Systemic States 

Dynamic Sentiments Motor States 

Moral Sentiments Social Situations 

In general, when a sentiment has once been aroused it per- 
sists, though less vividly, and attaches to the mental state 
which excited it, so that we " read the sentiment into " the 
objective situation : we characterize the object or event as real, 
true, beautiful, 'powerful, or good.^ This association of the sen- 
timent with the state which arouses it has led to much futile 
discussion as to whether an act is ' good ' in itself, whether a 
painting is ' beautiful ' when not observed, etc. There seems 
no doubt that sentiments are due to something specific in the 
inciting objects or acts; so that the latter may properly be 
called moral, esthetic, etc., as the case may be. But in many 
instances the same object or act arouses a different quality of 
sentiment in different individuals. It seems doubtful there- 
fore whether we should read the sentiment into the situa- 
tion which induces it without some reservation. Royce very 
properly distinguishes between the world of fact and the 
world of appreciation. The sentiments belong to the latter 
sphere of experience. 

Types of Sentiment. — The sentiment of realness, or real- 
ity feeling, attaches to perceptions of the outer world. We are 
' sure ' that the objects which we see, palp, heft, hear, etc., 
really exist. In ordinary perception this experience is mar- 
ginal. Like the familiarity feeling, it appears only as a sub- 
ordinate element in the perceptual state. In adult life the 
reality feeling rarely occurs as an independent experience. 

^ It is interesting to notice how frequently these adjectives or their equiva- 
lents are used for mere emphasis, without reference to the origin, in such 
phrases as "a real 6ne day," "a pretty accurate description," "a mighty well- 
written story," "a right satisfactory outcome." 



304 SENTIMENTS 

Occasionally it becomes a focal state when something which 
we see, hear, etc., is unlooked for and does not fit in with our 
general scheme of experience. If we meet a friend whom we 
thought a thousand miles away, the reality feeling bursts 
through into prominence. On the other hand in day-dream- 
ing, or when we are dazed by a sudden blow or a loud noise, 
the reality coefficient is often quite lacking — things about 
us do not impress us as real. In certain pathological condi- 
tions the sense of reality disappears entirely: the patient 
declares that nothing around him seems to be really existent. 

Belief is similar to reality feeling. The perceptual compo- 
nents are replaced by ideational elements. We are ' sure ' 
that certain of our images and thoughts are true. Owing to 
our ability to picture and represent things which are not true, 
two varieties of belief have developed. We may either be- 
lieve in the existence of the object thought of, or we may be- 
lieve that such an object does not exist.- We may believe in 
the truth of a generalization or in its falsity. When one pic- 
tures a mermaid, the sentiment attaching to the image is a 
belief in its falsity, while if we picture Vesuvius the sentiment 
takes the form of belief in the truth of the representation. In 
these two cases the sentiment is of the same general nature 
(belief) but the tone of the two is different. The difference 
is not in the feeling, but in the attitude which we assume (ch. 
xvii). The appreciative attitude of 'not' gives a special 
tinge to disbelief. Doubt is another species of sentiment 
aroused by ideational states, and is the true opposite of be- 
lief. Doubt arises from alternation of the two varieties of 
belief: truth sentiment and falsity sentiment. 

Esthetic sentiments arise indirectly from perceptions. In 
certain perceptions the feeling tone is especially prominent, 
and this systemic element combines with an idea of har- 
mony or value. This combination of feeling and idea at 
times becomes focal, and is experienced as an independent 
mental state. Esthetic experiences include sentiments of 



TYPES OF SENTIMENT 305 

beauty or harmony, and ugliness or discord. The two oppo- 
site varieties are distinguished by the nature of the feehng 
tone — in one case pleasantness, in the other unpleasantness. 
The intensity of the esthetic sentiments varies greatly with 
the individual and with training. In some individuals the 
appreciation of beauty, harmony, etc., appears early in life 
and develops without any special training; in others it is 
attained gradually, through education and imitation. The 
prevalence of esthetic sentiment is characteristic of the ' ar- 
tistic ' type of personality. 

Dynamic sentiments have been less carefully studied than 
the other types. They arise when the kinesthetic elements in 
perception become unusually prominent. When an intense 
feeling tone is joined to an idea of power the result is a 
dynamic sentiment. The kinesthetic sensations, it will be re- 
called, are stimulated by the activity of our own muscles; but 
their intensity varies with resistance to movement, which is 
due to forces in the environment. These two factors, the 
interna] and external, are represented in the qualities of dy- 
namic sentiments. Where the internal stimulus is dominant 
the sentiment is one of -power, or ability to act. Where the ex- 
ternal resistance is strong, the sentiment is one of opposition, 
of being thwarted, of force or poiver in the environment. The 
extreme case gives rise to the sense of the inevitable. At times 
dynamic and esthetic sentiments combine into a mental state 
called the sentiment of the sublime. 

Moral sentiments arise from the feelings which attach to 
our perceptions of social acts — usually those of other per- 
sons. Certain acts arouse approval, others arouse disapproval. 
This feeling is combined with the idea of social value and 
becomes a moral sentiment. There are two principal classes, 
the sentiment of right and the sentiment of wrong. Where the 
sentiment attaches to the whole conduct of any individual it 
is termed good or bad. 

Role in Mental Life. — Sentiments figure as the least im- 



306 SENTIMENTS 

portant type of mental states in the sum-total of our experi- 
ences. If a sentiment is weak it remains marginal and has 
little influence. If it is intense it tends at once to some motor 
discharge, which introduces the kinesthetic factor; in this case 
it ceases to be a sentiment and becomes an emotion or a vo- 
lition or an ideal. 

We do not usually rest with a mere sentiment of condemna- 
tion or approval. We are apt to start in, hand and fist, to 
remedy the wrongs which we condemn. We ' push along ' a 
good deed, literally as well as figuratively. Moral sentiments 
pass over into action and become volitions or expressions of 
our ideals; esthetic sentiments, if they are strong, pass over 
into emotion; dynamic sentiments arouse activity as we strive 
to overcome resistance or to express our ability and assert 
our power. 

In other words, sentiments lack stable equilibrium; if they 
are weak they are crowded out of focus by other states; if 
they are intense this very strength transforms them into 
other states. Beliefs are the most stable of all sentiments. 
They may persist through life, undergoing transformation and 
change of quality from time to time, but without losing their 
essential characteristics as sentiments. 

3. Volitions 

Nature of Volition. — Volition is a type of mental state 
in which conative and imagery elements are combined; it is 
due to the summation of kinesthetic stimuli and ideational 
impulses. In human beings perception frequently does not 
lead immediately to motor discharge. The central impulses 
which we observe as perceptions pass over into higher central 
neurons and produce imagery or other ideational states. The 
motor discharge, when at length it occurs, is ideomotor.^ 

In human mental life it frequently happens that the idea- 
tional state which immediately precedes the motor impulse 

1 See p. 288. 



NATURE OF VOLITION 307 

is an anticipation image — it represents some future move- 
ment. There is no structural reason why an anticipation 
image should issue in the appropriate movement. When we 
have an idea of moving our hand and grasping a book, the 
motor discharge might lead to various other sorts of action, so 
far as the inherited central connections are concerned. There 
is at most a broad regional connection between the sensory and 
motor centers. The centers for touch and motor discharge 
lie close together in the Rolandic region, and the specific center 
for touch in each part of the body lies opposite the motor center 
for the corresponding locality; but further than this there is 
apparently no structural correspondence. At the outset the 
idea of grasping a book might result in quite inappropriate 
muscular contractions and movements, such as withdrawing 
the arm or extending the fingers. 

In the course of our early life, by trial and error, the * in- 
appropriate ' responses are inhibited, and responses which cor- 
respond to the anticipation images are acquired. In other 
words, our actions come to be like our anticipation images 
through natural selection. When we picture raising the 
head, that very action follows; when we picture tracing the let- 
ter m with a pen on paper, our hand and fingers actually per- 
form the movements which we have imaged. 

The mental state which issues in these appropriate coor- 
dinated movements is not purely ideational. It is a combina- 
tion of imagery with kinesthetic sensations. This type of 
secondary mental state is called volition or will. 

In the older psychology volition was treated as an original 
datum of consciousness, or as a primary faculty of mind which 
initiates action independently of central nervous conditions. 
Experimental evidence goes to show, on the contrary, that it 
is a secondary mental state due to combination of two differ- 
ent sorts of data, that it arises through chance neural connec- 
tions, and that its appropriateness is due to natural selection. 
A crucial experiment by J. H. Bair on learning to move the 



308 VOLITIONS 

ear may be cited. He found that no amount of intense effort 
or vivid picturing of the operation served to produce the 
actual movement. The idea led to various movements of ad- 
joining parts of the scalp. Electric stimulation of the ear 
muscles assisted in giving the image deJBnite location, but at 
first the only motor result was an ability to hold the muscle re- 
laxed against the contracting stimulus of the electric current. 
Gradually the control was extended through action of adja- 
cent muscles, till at length complete voluntary control of the 
muscle was obtained.^ The process was found to consist in con- 
necting up the motor paths to the appropriate muscle with 
habitual paths, and then gradually eliminating the latter from 
the circuit. 

Regarded as a central or mental state, volition consists 
of (1) an anticipation image or thought of certain movements 
and of the changes produced by them in the environment, 
and (2) a conative experience of kinesthetic sensations in- 
volved in these movements and in certain bodily positions 
incident to the act. The ideational components are derived 
from external data, the kinesthetic sensations are derived 
mainly from muscular tension and incipient movements. 

More than any of the mental states so far discussed, voli- 
tion is concerned with the motor discharge and muscular con- 
tractions which follow. It is essentially anticipatory. It is 
the first mental state in which the emphasis is to be placed 
on the action of the organism upon the environment; in all 
the types so far treated the receptive side is most prominent. 

Three phases of volition have proved fundamentally im- 
portant in mental life: voluntary activity, purpose, and vol- 
untary control. 

Voluntary Activity. — Voluntary activity is characterized 

by delay and choice. The delay or latent period which dis- 

tinguishes-voluntary from sensorimotor and simple ideomotor 

activity is due partly to inhibitory impulses and partly to the 

1 Psychol. Rev., 1901, 8, 474-510. 



VOLUNTARY ACTIVITY 309 

succession of central processes (ideas) which occur before the 
motor discharge takes place. 

Inhibitory impulses are an important factor in voluntary 
activity. The idea of a movement tends to pass over im- 
mediately into motor activity; but in certain cases the tend- 
ency is checked by an inhibitory impulse. I start to go out 
walking, but the impulse^ to open the door and go out is 
checked until other preparatory movements are made, such as 
putting on a hat or consulting memoranda. The latent 
period in which one idea succeeds another before action 
takes place is called deliberation. 

The selective character of volition {choice) is due to the 
complexity of the neural conditions. When the tendency to 
immediate response is checked, the voluntary state is often 
followed by another idea and conation, representing some al- 
ternative activity, and so on through a long series of volun- 
tary experiences. One of these at length becomes so strong 
that it leads to motor discharge and the result is an actual 
voluntary movement. When I get out of bed on a holiday 
morning my first ' plan ' is to spend the day reading in the 
library. The bright spring weather suggests the alternative 
plan of motoring through the country. The pressure of daily 
duties suggests finishing a half-written article. Finally, the 
thought of a long brisk walk, combining pleasure with exer- 
cise, proves the most powerful impulse, and my voluntary 
activity proceeds along this line. 

Volition is selective, not because it determines events 
which are otherwise ' indeterminate,' but in that it tends to 
bring about the fittest actions, rather than the most obvious. 
In any response the path of motor discharge is along the line 

^ In popular psychologj' impidse is used to denote a tendency to act based 
on internal motivation. The discussion in the preceding section indicates 
that this tendency is not 'innate' as is popularly supposed; accordingly this 
use of the term had best be avoided. In the illustration given here there 
is both a motor nerve impulse and an impulse in the popular sense of the 
term. 



310 VOLITIONS 

of least resistance, but in volition the central impulse under- 
goes a great variety of modifications before the path of dis- 
charge is opened up. 

Voluntary activity is acquired and perfected by means 
of the learning process (ch. vii). Instances of voluntary 
learning may be observed in the formation of general habits, 
such as reading, writing, singing, violin or piano playing, type- 
writing, or the like, when we follow a deliberative plan instead 
of proceeding by active trial and error. A specific or concrete 
habit, such as learning a certain tune, may also be acquired by 
voluntary deliberative selection. As a voluntary habit be- 
comes inground, its performance tends more and more to 
start without a preliminary period of deliberation and review- 
ing of the alternatives. A perfectly fixated habit is a pure 
conation. 

Purposive Factor in Volition. — The ideational factor in 
volition is called a forethought, plan, or purpose. It is the 
image or thought of a prospective action. If the act or move- 
ment pictured is later carried to completion the forethought is 
followed by a perception similar to itself. The forethought 
is a present anticipation image founded on past experiences, 
to which a future reference or projection is attached. 

Anticipation images or thoughts serve as bases for future 
actions on account of the uniformity of nature. Just so far 
as the circumstances are similar we may apply past experi- 
ences to future conditions; but if the circumstances are quite 
new, our forethoughts are usually quite vague. The thought 
of going to my laboratory leads at once to the appropriate 
movements of walking, turning, climbing, etc., because I have 
gone over the same path in the same way to the same place 
for many years. On the other hand when a young man is 
planning out his life career, the general situation and most of 
the circumstances are so different from anything in his past 
experience that his picture of the future is very indefinite; it is 
usually no more than a bare schematic outline. 



PURPOSIVE FACTOR IN VOLITION 311 

The distinguishing mark between a purpose-idea and other 
anticipation images is the prominence of our own activity in 
the purpose experience. Purposes are essentially representa- 
tions of our own actions. The ideas are not always kinesthetic 

— they may be visual or tactile; more often they are thoughts 

— mere verbal symbols rather than pictures of the act (ch. 
xv) . When kinesthetic sensations of effort or energy are at- 
tached to the purpose-idea, it is transformed into a volition. 
But even apart from these kinesthetic accompaniments the 
purpose-idea itself has a reference to the individual's own 
doings which is lacking in anticipation images generally. 

Some writers have claimed that volition contains another 
factor besides the purpose-idea and motor sensations. When 
voluntary activity is started the mental state is noticeably 
different from the preceding state of deliberation. This dif- 
ference has been attributed to a specific mental element called 
the fiat. It seems more than probable, however, that the fiat 
is merely an intense kinesthetic condition which belongs to the 
dominant alternative — not a distinct component. We do 
not find it in habitual actions, which proceed without 
deliberation.^ 

Voluntary Control; Role of Volition. — Control is the phy- 
siological process of coordinating motor activity by means of 
central adjustment. We may distinguish four types of central 
control: autonomic, instinctive, automatic, and voluntary.^ 

Autonomic control is adjustment of the organic processes, 
such as digestion, through the sympathetic or autonomic sys- 
tem. In some cases both the sensory and motor paths of the 
arc are through neurons of the sympathetic; in every case 
the motor paths belong to this system. The cerebrospinal 
system may modify autonomic activity through impulses 
which cross to the sympathetic in the sensory and central 
segments. 

^ See Appendix, "Conscious Purpose," p. 427. 

2 A fifth and higher type, rational control, will be treated in ch. XV. 



312 VOLITIONS 

Instinctive control is adjustment through arcs of the cere- 
brospinal system which are definitely and permanently formed 
when the first impulse passes through them. As we noticed 
earlier (ch. vi), these arcs are not fully formed before they 
come into actual use. But the central terminals of their sen- 
sory and motor paths are so placed by structural inheritance 
that when an impulse passes over the neurons the connection 
is made, since it proves to be the path of least resistance. 

Automatic control is sensorimotor or simple ideomotor ad- 
justment which is not structurally determined, but has been 
built up by ' trial and error.' It occurs when the central ter- 
minals of the sensory and motor paths have many branches, 
no one of which furnishes at all times a path of least resistance. 
The circuit actually joined up has already been formed by ac- 
commodation and fixation, and the operation is accompanied 
by a conative mental state. 

Voluntary control is complex ideomotor adjustment. Here 
the motor path is determined by a higher integration of im- 
pulses and by a succession of central states, among which are 
anticipatory ideas, or forethoughts, as well as kinesthetic 
states. 

As already stated, anticipation and forethought bring the 
individual's past life, and to a certain extent his future, into 
intimate connection with the present. The prominent feature 
of voluntary control is that the action is determined by the 
man's whole life, not merely by present situations. Our 
voluntary acts are the expression of our selves; we control them 
as personal beings (ch. xviii). It should be remembered, how- 
ever, that the precision of voluntary control varies according 
to our mental capacity, as determined by heredity and past 
experience. Any defect in the neural or terminal mechanisms, 
whether sensory, central, or motor, hampers the development 
of adjustment and limits the efficiency of control. The com- 
pleteness of control depends also largely upon the breadth 
of one's past experiences. These psychological factors are 



VOLUNTARY CONTROL 313 

to be taken into account in any ethical theory of responsi- 
bihty.i 

Vohtion is by far the most important of the secondary men- 
tal states so far examined. It plays a more prominent role 
in human mental life than any of the primary states, except 
perhaps perception. The broader working of control which 
arises in connection with voluntary processes, makes the in- 
dividual master of his environment to a higher degree than 
he can attain without it. Man foresees future dangers and 
responds in such a way as to prevent or overcome them. The 
ascendency of the express^ive side of experience is increased 
still further in man by language and rational activity (ch.xv). 

Collateral Reading : 
James, W., Psychology, chs. 24, 26. 

Titchener, E. B., Text-Book of Psychology, sees. 128-137. 
Angell, J. R., Psychology, chs. 18-20. 
Calkins, M. W., First Book in Psychology, chs. 11, 12. 
Pillsbury, W. B., Fundamentals of Psychology, ch. 14. 
Jastrow, J., Temperament and Character, ch. 3. 
McDougall, W., Social Psychology, chs. 3, 5, 6. 
Crile, C. W., Origin and Nature of the Emotions, pp. 77-156. 
Cannon, W. B., Bodily Changes in Pain, Hunger, Fear and Rage. 
Dewey, J., Psychology, chs. 18-22. 

Thorndike, E. L., Ideomotor Action, Psychol. Rev., 1913, 20, March. 
Washburn, M. F., Movement and Mental Imagery, chs. 8, 9. 
Warren, H. C, A Study of Purpose, J. of Philosophy, 1916, 13, nos. 1-3. 

Practical Exercises : 

Describe the expression of three different kinds of emotion in cases you 

have witnessed recently. 
Analyze some powerful emotion of your own at the time or soon after 

the outburst has subsided. 
Examine your experiences when you plan some course of action, such as 

how to spend a holiday. 

' See Appendix, "Free Will, Determination, and Responsibility," p. 431. 



CHAPTER XV 

SECONDARY MENTAL STATES (continued) 
4. Thought and Language 

Distinctive Features. — Thought and language combine 
ideational and kinesthetic elements. To this extent they 
resemble volition. They differ essentially from volition and 
from all other mental states so far discussed in two distinctive 
characteristics : (1) Their ideational components are symbolic. 
(2) Their development is due almost wholly to the social en- 
vironment; that is, they arise through the interaction of indi- 
viduals with one another. 

A further characteristic is that thought and language 
develop together, each furnishing material for the other. 
Thought is an outgrowth of imagery due to the addition of 
kinesthetic elements, while language is an outgrowth of cona- 
tion with the addition of symbolic ideational elements. In 
thought the kinesthetic element is less prominent than the 
ideational, and in language the ideational element is less 
focalized than the kinesthetic. Thought and language are 
complementary states. Increased definiteness of thought 
leads to more dejfinite expression in language, while a new ver- 
bal symbol is apt to make for greater precision of thought. 

Symbolic Character. — In discussing imagery (ch. xiii) we 
found that a memory image is virtually a reproduction of some 
perception; a general image is a mental state reproducing cer- 
tain characters which are common to a number of similar per- 
ceptions; images of the remaining types reproduce characters 
drawn from several perceptions which may or may not be 
similar. A distinguishing mark of all imagery is that it re- 
produces certain features which have previously appeared in 
perception. 



SYMBOLIC CHARACTER 315 

Various elements which were not in the original perception 
of an object become associated with the image. We may re- 
gard a thing as beautiful, and a systemic element is thereby 
attached to the idea. If we picture it as to be avoided or acted 
upon by ourselves, the image is transformed into a purpose or 
volition. In the same way it comes about that certain purely 
arbitrary kinesthetic elements called names attach to images 
of every sort. In adult life the idea of my chum is not a mere 
image; the name ' Walter ' is an integral part of the expe- 
rience. The general idea of the leading domestic animal is 
not simply a general image, but an image to which the name 
*dog' is attached. 

A name is essentially a kinesthetic experience, though audi- 
tory and visual elements are usually included with the motor 
components. Names are first spoken or written or gestured; 
they are associated with images or perceptions, and in the 
course of time they become integral parts of the ideational 
experience. We call them symbolic or arbitrary, because they 
rarely belong to the original perceptual experience; they are 
not part of the external objects which stimulate us. 

Arbitrary kinesthetic elements similar in sort to names 
are attached to other mental states and to their components. 
The whole group of arbitrary kinesthetic associates are 
called words, and the combination of words with idea- 
tional elements is called language or thought, according as 
the kinesthetic or ideational components are the more prom- 
inent. 

For reasons that will appear presently, these arbitrary 
components tend in the course of time to become focalized. 
They come to be practically the whole material of the mental 
state ; — the image components which reproduce the charac- 
ters of the external object remain only as marginal accompani- 
ments. The experience is no longer a picture or replica of 
the object, but a symbol, which may bear no resemblance to 
it whatsoever. 



316 THOUGHT AND LANGUAGE 

Social Origin. — The genesis and growth of language is due 
entirely to the social relations among members of the species. 
The sole utility of language lies in the fact that it furnishes a 
medium for communication between one individual and an- 
other. When I utter the word dog or any other word, it is in 
order to arouse in some other individual an idea or series of 
ideas corresponding to my own thoughts. It is safe to as- 
sume that language would not have developed if mankind had 
not lived in groups. 

Thought is not so essentially social. We think to ourselves 
in symbolic terms, without reference to the effect on others. 
But it is dijBBcult to see how thought could have developed 
without language — that is, without a social environment. 
Apart from social conditions there is nothing in mental life to 
make the symbolic element of an idea vivid or focal. Objects, 
situations, and events furnish the original stimuli. Ideational 
states are determined by the character of the sensations which 
these stimuli arouse. Some components in the ideas become 
increasingly focal, but the vivid elements are pictures of ex- 
ternal things or occurrences — not symbols. The non-social 
idea of ' dog ' is the dog's general appearance, his bark, his 
bite, his characteristic modes of behavior; all of these are 
schematic reproductions of actual sensations arising from 
' dog-stimuli.' 

The need for a name is social. We have not always a dog 
to point to; we can imitate his bark, but not (satisfactorily) his 
hunting activities. One of the older theories of the origin of 
language was based on man's imitation of barking, crowing, 
mewing, etc. This theory meets difficulties when it comes to 
the naming of fish, fruit, and other ' voiceless ' or inactive 
things. To designate such objects to other persons, and to 
indicate events and human activities, arbitrary gestures or 
sounds seem to have been required from the start. Imita- 
tive (onomatopoeic) names tend to become conventional- 
ized also. Since these kinesthetic symbols are reproducible. 



SOCIAL ORIGIN 317 

they are highly useful for communication between man and 
man. They are easier to focalize and control than images. 
Through repetition they attain greater prominence as com- 
ponents in the ideational states. Hence the symbolic ex- 
perience of thought has tended more and more to supplant 
imagery in civilized life. 

The history of the human race indicates that man rarely 
invents words except under stress of social communication. 
Things, creatures, and qualities which have social signifi- 
cance are the first to receive names. The degree of social 
development of a race may be roughly estimated by the size 
and character of its vocabulary. 

Mutual Dependence. — It is evident from this that thought 
and language are mutually dependent. The demands of 
social communication lead to symbolic naming, which takes 
the form of kinesthetic experiences. These kinesthetic sym- 
bols attach to the ideas and transform them into a new kind 
of mental state. In the type of behavior called communica- 
tion the kinesthetic component is stronger than the idea- 
tional, and the mental state is language. When the same 
symbol occurs without communicative expression the idea- 
tional component is stronger than the kinesthetic, and the 
mental state is thought. 

The growth of each one of these states means the growth of 
the other. New words add precision to thought. Growth of 
definiteness in thought leads to the appearance of new words in 
the language. 

It is perhaps too sweeping to say that thought could not 
arise or did not arise in any race or individual without lan- 
guage, or that language never appeared without symbolic 
ideas. The examination of known races leads to the con- 
clusion, however, that the development of either of these 
states beyond a rudimentary stage depends upon the coopera- 
tion of the other. 

Types of Language. — The chief types of language are 



318 THOUGHT AND LANGUAGE 

gesture, speech, and graphic record. ^ Facial expression is more 
primitive than any of these, but it is confined to emotional 
states and does not seem to have attained any symbolic de- 
velopment. Such communicative expressions as winking an 
eye or contorting the face may be regarded as facial gestures. 

Gesture language is probably more primitive than speech. 
It arose from the practice of pointing to objects or waving the 
arms to arouse attention. In time some of these gestures as- 
sumed a conventionalized form. Certain movements of the 
hand or head came to denote fish, fruit, fire, cooking; pairs of 
opposite movements came to signify assent and dissent, or 
* come here ' and ' go away.' A developed form of gesture 
language is used in civilized communities among the deaf. 
Otherwise it occupies a secondary positioUj being superseded 
almost wholly by speech. 

Vocal expression (speech) is so much more convenient than 
gesturing that it has developed far beyond the latter. One 
can readily talk when engaged in fishing, plowing, etc., 
while gestures disturb these occupations. One can listen to 
oral conversation without turning the head; it is not so easy 
to watch the plow and a companion's gestures at the same 
time. The ears are always open; we can secure a man's at- 
tention by speech without stepping in front of him or seizing 
hold of him. 2 In the sick room or in No Man's Land gestures 
are more effective than speech. But in normal conditions of 
life speech has generally far greater advantage. 

The graphic form of language is used in civilized communi- 
ties to supplement speech. It consists in making permanent 
marks or impressions upon stone, bricks, papyrus, and paper. 
In the older graphic languages the records were rude pic- 
tures of objects; later these pictures became conventionalized, 

^ As modes of behavior they are called gesturing, speaking (or talking), 
and writing. 

* The button-holing habit is possibly a survival of the primitive gesture 
stage. 



TYPES OF LANGUAGE 319 

as in Chinese, or each graphic unit symboHzed a syllabic sound, 
as in syllabary Japanese. In the graphic language of modern 
western races each symbol (letter) represents an elementary 
vocal sound, either consonant or vowel. The whole group 
of different letters comprise the alphabet. The letters of the 
alphabet symbolize vocal sounds which are themselves arbi- 
trary symbols. 

There are several varieties of graphic language, whose dis- 
tinction is more important from the social than from the purely 
psychological standpoint. Besides ordinary handwriting we 
may mention printing, typewriting, telegraphy, and pho- 
nography. In all these forms the characteristic feature 
is the permanent record, which makes it possible for an in- 
dividual to communicate with others at great distances and 
after long intervals of time. In fact, the chief role of graphic 
language is to extend the range of communication in space 
and time. Graphic language, like gesture language, is re- 
ceived visually, except the phonographic variety, which is 
auditory. 

Nearly all graphic languages are asymmetrical. In the 
Greek and Latin alphabets the record always runs from left 
to right, in Hebrew and Arabic from right to left, in Chinese 
from top to bottom. The order is practically never reversed, 
nor are individual letters turned around.^ ' Mirror-script ' is 
unintelligible to most individuals who attempt to read it,- and 
it is equally hard to write. Experiment shows that this dif- 
ficulty is due merely to long fixation of habit; one can in time 
learn to write and read reversed script quite readily. 

^ By way of exception the Egyptian hieroglyphics run either left-right, 
right-left, or down the page. As the characters are mostly human or ani- 
mal forms one can determine at a glance how to read the record — we 
meet the figures jace to face, unless the characters run in columns, in which 
case we read downward. Egyptian writing (and reading) as a motor pro- 
cess is therefore horizontally symmetrical, though the separate characters 
are nearly all asymmetrical. 

* See Fig. G7, p. 266. 



S^O THOUGHT AND LANGUAGE 

The asymmetry of graphic language is due to the preference 
of one hand (usually the right) over the other in intelligent 
acts; and this is in some way connected with the greater de- 
velopment of certain higher centers in one hemisphere of the 
brain. The speech center in most individuals is located in 
the left hemisphere, which controls movements in the right 
side of the body. The origin of the specific direction of writing 
may possibly be connected with the instrument used: a quill 
is more easily pulled along; a chisel is more effective when 
pushed; a brush is more naturally swept down toward the 
writer. 

Comprehension and Reading. — Communication is a two- 
sided affair. It is not completed, hke other types of behavior, 
when the reaction or response is made. It involves a later 
receptive process on the part of another being. The spoken 
word produces complex sound waves, which serve as a verbal 
stimulus to the auditory receptor. The central and con- 
scious effect on a second person is very different from that 
of other compound clangs. The sensory components of the 
experience are very indistinct. They serve mainly to arouse 
an ideational state, which is a thought similar to the thought 
experienced by the first person in speaking the word. The 
mental process of receiving verbal stimuli derived from 
speech or gesture is comprehension.^ It results in an ideational 
state which is usually a thought, though at times it may be 
an image. 

The graphic record produces a visual stimulus. The re- 
ceiving process is much the same as in comprehension, except 
that the succession of experiences is more under the control 
of the second person. By moving the eyes slowly or rapidly 
he can regulate the speed with which the verbal stimuli are 
presented. The receptor process for graphic stimuli is called 

^ Oddly enough there is no English word which denotes the process ex« 
actly. Comprehension is used here in a slightly technical sense. Under- 
standing includes both comprehension and reading. 



COMPREHENSION AND READING 321 

reading. The resulting mental states are thoughts with 
occasional imagery. 

The distii;iction between ordinary sensory stimuli and 
verbal stimuli is important. The physical material is the 
same in both — sound waves or light waves; but their central 
effect is radically different. This is illustrated if we have 
some one read us selections from a book in some unfamiliar 
language, interjecting here and there an English phrase. Or 
we get the effect when we glance over the pages of a Japanese 
book with an occasional English quotation.^ 

Nature and Types of Thought. — The ideational states of 
civilized man consist almost wholly of thoughts. The word 
* horse ' is for most of us the dominant feature of the horse- 
idea. We picture vaguely the appearance of horses, their 
movements, the sounds which they make in galloping or 
neighing; but the central feature in our idea of a horse is the 
name or word. 

For some individuals a word is preeminently a sound 
('Horse!'). For others it is the adjustments of throat and lip 
muscles, with the kinesthetic sensations which they arouse. 
For others it is the printed word as it appears to the eye; or 
it may be the kinesthetic sensations of writing the word. In 
many cases the experience combines two or more of these 
factors. When we think of a horse the verbal symbol of 
whatever sort forms the chief component of the thought — 
the other elements lie dim in the backgi-ound. In abstract 
thinking (2 + 2 = 4) verbal symbols constitute practically 
the whole experience. 

Since words bear no similarity to the objects for which 
they stand, they are better material to work with than general 
images. When new varieties of a given species are discovered 
the general image may require considerable reconstruction, 

^ Reading aloud is a further complication of the communicative process. 
The reader acts as a 'relay' between the imparting and the receiving indi 
viduals. 



322 THOUGHT AND LANGUAGE 

but the verbal name does not. The general image of ' swan ' 
had to be quite made over when black swans were discovered, 
but the word was unchanged, except for adding a ' dot of 
black ' to the mental background. 

In civilized man general imagery tends to be supplanted 
by symbolic images or thoughts. Your idea of specific ob- 
jects and beings may be a free image, with the name a minor 
feature of the experience. The idea of your chum, your dog, 
your watch, is probably a sort of composite picture of many 
perceptions; the name William, Rover, ' my watch ' is a 
relatively unimportant element. With ideas of general 
classes or sorts of things or events the opposite is true. Here 
it is not the general image, but the symbolic name that plays 
the chief role. When you think of paper, stairs, piano, 
dressing, eating dinner, etc., the image of the thing or act 
is relatively unimportant — the word is the dominant part 
of the experience. The association between the name and 
its object is firmly fixed in the individual because it prevails 
in the community generally. The arbitrary nature of words 
appears strikingly when we move into a community where 
an unknown language is used. 

Imageless Thought. — Recently there has been consider- 
able discussion among psychologists in regard to ' imageless 
thought.' A number of careful investigators report that 
their thoughts lack entirely the character of imagery. Others 
are inclined to question these reports. The conflict of opin- 
ion is probably due to different interpretations of the term 
imagery. Popular usage applies the term almost wholly to 
visual data. In psychology organized auditory, tactile, and 
kinesthetic ideas, so far as they exist, are called images. But 
the kinesthetic verbal elements may not be images at all; 
they may be actual sensations. It is quite possible that for 
some individuals thought consists wholly of kinesthetic sen- 
sations — or nearly so. For such persons the thought of a 
horse may consist of adjustment of the larynx and other 



IMAGELESS THOUGHT 323 

vocal muscles preparatory to uttering the word ' horse.' It 
is then a sensory mental state, not an image. 

For most persons ' external ' ideas of sight, hearing, and 
touch enter into the thought experience. When any sum- 
mation of nerve impulses occurs, modification takes place. 
On the subjective side, when any combination of mental data 
occurs there is a process of transformation. Hence, as 
thoughts develop the components are gradually transformed, 
till at length the ' thought ' state comes to be wholJy unlike 
the ' image ' state from which it is derived. This is especially 
the case if several different types of imagery enter into the 
thought. In the end the thought is likely to lose the dis- 
tinctive character of each type; the experience then becomes 
a composite, in which the several sense-modes are fused to- 
gether into a new quahty. One may readily test whether 
this is true in his own case by examining certain typical 
thoughts. Possibly ' imageless ' thought is due to this trans- 
forming process. The original image components may be- 
come so transformed in the course of time as to lose all 
recognizable semblance to any sense qualities. 

Meanings and Values. — The experience called meaning 
is part of the thought state. Meaning comprises those ele- 
ments in the thought which are not symbolic, but which 
resemble the object or situation. When we think of man the 
symbol or word forms the central feature (focus) of the ex- 
perience. Along with the word there may be in the back- 
ground or margin of the thought a fleeting image of some 
specific man or of certain human characteristics. These 
non-symbolic factors in the experience constitute the meaning 
of the thought. 

When the neural impulse which we observe as a thought 
experience occurs in the brain, these image components are 
aroused simultaneously with the symbolic elements; they 
give a " tinge of reality " to the experience. This imagery 
tinge is the meaning consciousness. In other words, the 



324 THOUGHT AND LANGUAGE 

meaning of a thought comprises those elements in the ex- 
perience which correspond to the object or situation, as dis- 
tinguished from the mere verbal or symbolic elements. When 
we endeavor to examine the meaning of a word, what hap- 
pens is that these marginal elements become focalized. 

The psychological character of meaning may be observed 
by comparing the mental state aroused by ' meaningful ' 
words with nonsense. There is a vivid tinge of imagery for 
most of us when we see or hear such words as sacrament and 
delicious, which is missing in luntosity and pelegation. No 
meaning attaches to the visual presentation of the sentence: 
"Isle of use wheat tart "; but the auditory presentation of 
the same sentence fairly glows. 

Psychologically speaking, the value experience is similar 
in type to the meaning experience. Meaning comprises the 
ideas of certain qualities of an object or event; value consists 
of ideas of intensity, duration, and other quantitative char- 
acters. We stated that an image differs in intensity from the 
perception which it represents. The same is triie of a thought. 
We can compare the intensity of two perceptions, feelings, 
or conations, and repeat the comparison in imagery and 
thought. If we associate the words ' six ounces ' with one 
lifted weight and the words 'four ounces' with another lifted 
weight, we have the wherewithal to compare the inten- 
sity of these two experiences when they are reproduced as 
images or symbolized as thoughts. Such quantitative ideas 
are attached to perceptions, images, and thoughts. They 
usually enter into thought experiences as mere marginal 
elements and constitute the value-coefficient of the experi- 
ence. When we think of an object or event a slight ' value 
tinge ' attaches to the symbolic word, in the same way as the 
meaning tinge attaches to it. This is especially the case with 
thoughts in which quantitative characters are prominent. 
My thought of a certain book is usually tinged with some 
such ideational elements as large or small, long or short, 



MEANINGS AND VALUES 325 

difficult or easy reading, true or false. When these idea- 
tional elements become focal, the state becomes a value ex- 
perience. 

Value experiences which involve social situations are gen- 
erally rich in systemic components. The thought of a good 
or a bad action is generally accompanied by the feeling of 
desire or aversion. There is also in most cases a kinesthetic 
tinge other than the language component. We tend to act 
upon the value experience. Where these hedonic and ex- 
pressive components are focal, the experience is no longer a 
thought, but belongs to the class called ideals, which will 
be discussed presently. Some writers confine the term value 
to this higher mental development. But value experiences 
of the higher type appear to be essentially the same as the 
thought of long or short, quick or slow, etc.; they are best 
understood when regarded as an outgrowth of these lower 
stages. 

It should be noted that the ideational values of an ex- 
perience may be quite different from its perceptual or sensory 
values. A ' trivial ' event from the perceptual standpoint 
may ' loom big ' in our scheme of life when regarded from 
the standpoint of thought and social rela,tions. And again, 
the ideational value of an experience may vary widely in 
different circumstances. At one time we may attach slight 
value to some event, such as the killing of a usurper; later we 
may come to regard it as a turning-point in history. 

It appears, then, that there is not so close a correspondence 
between the ' objective ' values of situations and events and 
our subjective experiences of value in the sphere of thought, 
as in the sphere of perception. As psychologists we deal 
only with the value experience; it belongs to the economist, 
the artist, and the moralist to adjust our appreciation of 
situations and events to the ' values ' of objective reality. 

To sum up, meaning and value are primarily those elements 
in the thought which correspond to the object or situation 



326 THOUGHT AND LANGUAGE 

outside of ourselves which aroused the original perception. 
Meaning is the component in an experience which corre- 
sponds to qualitative characters of things, while value cor- 
responds to their quantitative characters, such as intensity, 
duration, size. As our thought life advances, the feelings, 
conations, and social situations induced by perceptions take 
on meaning and value elements also. In most ideational 
experiences the meaning and value components are obscure 
and marginal, but at times they become attended to or 
focalized. This leads to the specific types of thought known 
as meaning and value experiences. The thought itself may 
be not of a man, but of his ethical value; we may think not 
of a political procession but of its social significance. 

Rational Thought ; Concepts and Judgments. — Concep- 
tion and judgment constitute a higher level in the develop- 
ment of thought. These states are known as rational thought. 
In rational thought the meaning elements or the value ele- 
ments become focalized; the verbal elements do not become 
marginal, but they are less distinct than in ordinary thought. 

The thought of an object or event in which the meaning 
or value is thus focalized is called a conception or concept. 
When I think of a horse with the meaning uppermost, certain 
characters, such as vertebrate, ungulate, wagon-pulling, do- 
mesticable, are in the focus of the experience. The concept 
of horse is a thought in which some or all of these meaning 
elements are more vivid than the verbal symbol. When I 
think of four or short or stocky the thought is a value con- 
cept. 

A judgment is a mental state which combines two concepts, 
that is, two meaning or value elements, both of which are 
focal. The fusion of two thoughts does not constitute a 
judgment unless some of their meaning elements are similar. 
The thought of man combined with the thought of a horse 
may produce the thought of a centaur, but this is not a judg- 
ment. If, however, we combine the concept of horse with 



RATIONAL THOUGHT 327 

the concept of vertebrate, we obtain the judgment " Horse — 
vertebrate," — or as it is generally expressed in language, "A 
horse is a vertebrate," or, " All horses are vertebrates." 
When we think of a certain light and of intensity and com- 
bine the meaning with the value, the resulting thought is the 
judgment, " This light is bright." 

If both of the focal elements are meanings the experience 
is called a meaning judgment, if one is a value, the experience 
is a value judgment. Judgments are also classed as particular 
or universal, according as the leading component is due to a 
single perceptual stimulus or is a generalized thought derived 
from many experiences. In particular judgments one of the 
focal components may be a perception, instead of an idea. 
Here is an exceptional case, in which a perception forms part 
of a secondary mental state. 

Since thought tends to expression in language, both types 
of rational thought have corresponding types of rational ex- 
pression. The language equivalent .of a concept is a term; 
the equivalent of a judgment is a proposition. The thought 
' horse — black ' as a judgment may be instantaneous, but 
as a proposition the experience begins with one term and the 
other term arises later. This experience involves succession 
of mental states (ch. xvi). 

In examining these higher developments of thought the 
psychologist is concerned only with the nature of concepts, 
judgments, terms, and propositions as mental states, not 
■wdth the science of logic as such. If our analysis is correct, 
a mental judgment does not consist, as many logicians be- 
lieve, in the discovery of relationships among ' classes.' As 
a subjective experience a judgment is a combination of cer- 
tain meanings or values which attach to thoughts. A prop- 
osition is the expression of this rational experience in lan- 
guage. The formation of concepts depends upon similarity 
in meanings or values, and this similarity may usually be 
traced back to similarities among perceptions. 



328 THOUGHT AND LANGUAGE 

Role of Thought and Language in Mental Life. — It ia 
scarcely possible to exaggerate the importance of thought and 
language in the mental life of man. On the receptive side 
they give a finishing touch to the integrative process; on 
the motor side they perfect the coordination of activity to a 
far greater degree than conation and volition. They trans- 
form the central adjustment process into rational control. 
They furnish two new modes of intelligent behavior, com- 
munication and rational expression of thought, over and above 
the trial-and-error learning of subhuman species. Taken 
together they provide a tremendously ejOFective mechanism 
for the adaptation of response to the conditions of the 
environment. 

More than any other mental state except perhaps emotion, 
thought and language must be studied in the light of their 
history. But whereas emotion is a survival from ancestral 
conditions, thought and language are brand-new human 
acquisitions. They are still in the making. 

An important feature in the growth of language is its slow 
evolution in the race and its rapid development in the in- 
dividual. New words arise phylogenetically by a gradual 
process, as the sphere of thought in the race enlarges. Once 
adopted they are transmitted to the bulk of individuals in 
the community and are readily learned by children or ado- 
lescents. Much the same is true of thought. The growth 
of thought depends intimately upon the existence of words. 
If the vocabulary of a community is scanty its range of 
thought is limited. Given a rich vocabulary, the best organ- 
ized individuals in the race quickly attain a wide range of 
thought. In the sphere of thought, more than in any other 
type of mental state, we find tremendous individual differences 
in capacity and development. Such differences appear es- 
pecially in the realm of rational thought. 

The development of thought and language in the individ- 
ual depends not only upon the social environment, but 



ROLE IN MENTAL LIFE 329 

upon inherited nerve structure. To bring about these men- 
tal states the higher receptive centers must be connected 
by association tracts with various motor centers. Gesture 
language depends for its development upon the ready es- 
tablishment of connections between the visual center and 
the center for arm and hand movement. Vocal language 
involves inherited pathways between the auditory centers 
and the centers for vocal expression. Writing involves 
pathways between visual or auditory centers and those for 
finger movements. The intricate inherited organization of 
the human cortex accounts for the superiority of the human 
cognitive life over that of lower species. 

5. Ideals and Rational Actions 

Their Nature and Classification. — Ideals and rational 
actions are the most composite of all mental states. They 
combine ideational, hedonic, and kinesthetic elements. In 
general the ideational components are most prominent. The 
social factor ordinarily plays an important part in forming 
these states, but they are not essentially social like thought 
and language. 

An ideal consists of a vivid image or thought, which is com- 
bined with an intense feeling and with intense kinesthetic 
elements. If one's ideal is to become a teacher, he has a 
general image or usually a highly complex thought of the 
various characteristics of this profession; he is also stirred 
by a noticeable feeling when he thinks of it; and his acts 
with their kinesthetic accompaniments are such as will tend 
to fit him to become a teacher. In other words, an ideal 
involves thinking a thing, feeling it, and doing it. 

Usually our ideals develop gradually out of particular ex- 
periences in which one or other of these elements predomi- 
nates. The experiences which lead to ideal-formation are 
largely social. We are told by parents and friends that we 
are fitted for a certain career; an ideal is aroused by our con- 



330 IDEALS AND RATIONAL ACTIONS 

tact with someone who has been successful in this direction, 
or is inhibited by some conspicuous failure. 

An ideal is the outgrowth of many separate experiences. It 
is a ' composite picture ' of many thoughts, volitions, senti- 
ments, and emotions, all of which bear upon one and the 
same type of situation. For these reasons our deepest- 
rooted ideals have usually grown up slowly and are related 
to a host of separate experiences. The elementary constitu- 
ents of ideal states are often present as marginal components 
in the general ' stream ' of mental life. These marginal ideals 
determine our motor expression; they are termed motives of 
action. Only on occasion do ideals become focal, so that 
we are intensely aware of our general aims in hfe. 

Ideals are classified according to the type of mental state 
which predominates among their components. They include 

Scientific ideals 

Esthetic ideals 

Ideals of power or accomplisTimCTit 

Moral and religious ideals 

Ideals occur in various degrees of subordination. Highest 
of all is our ' life ideal,' which marks the general trend of our 
career. Beneath that may be the ideal of some specific line 
of work. Subordinate to this is the ideal of our general course 
of action during the next few months or years. Lowest of all 
are specific ideals or motives of daily action. In both higher 
and lower ideals the dominant factor may be scientific, es- 
thetic, or dynamic, as well as moral. Owing to the domi- 
nance of social organization in modern life, moral ideals 
rank highest in importance. But a study of mental life 
shows the presence of other types to a greater extent than 
is ordinarily recognized. 

In civilized man the thoughts which enter into ideals are 
generally rational thoughts. Hence, when an ideal issues in 
motor expression the resulting mental state belongs to a higher 
level than volition; it is called rational action. Civilized man 



THEIR NATURE AND CLASSIFICATION 331 

acts systematically, in accordance with certain general ra- 
tional principles which grow out of rational thought; his 
scheme of action may be scientific or esthetic or practical 
or moral. These general principles are formulated in the 
organized branches of learning called science, esthetics, 
practical training, and ethics. But even apart from the 
definite formulation of general principles our activities tend, 
as they become organized, to rest upon judgments instead 
of ordinary thought. That is, human activity tends to be- 
come rational. 

Even the uneducated man acts to a certain extent ra- 
tionally. When he breaks an arm or dislocates an ankle 
he calls in a surgeon; he is not content, like his primitive an- 
cestors, to hang an amulet over the injured member or rely 
upon magic words to effect a cure. When he sets out to be- 
come a mechanic he takes a course of preparatory training 
instead of learning by mere trial and error. And the same in 
any branch of artistic activity. 

In the sphere of social action the rational character is even 
more fundamental. We do not hesitate to eat food near a 
marble statue, but we shrink from eating near a starving man. 
Human beings in whom rational thought life is well devel- 
oped act with constant reference to the social environment. 
Their actions are influenced by the thought that other men 
are beings like themselves. Their behavior assumes a new 
and higher type, called social or moral conduct. 

Not only is our own behavior modified by rational thought 
and by our thought of others, but we appraise the actions of 
other men according to the same standard. We judge their 
behavior with reference to rational and social conditions. In 
other words, we appraise human activity not as a series of 
instinctive or mechanical movements, but as examples of 
rational actions and more especially as social conduct. 

Summary of Mental States. — The elementary data de- 
rived from the external, systemic, and motor senses, and the 




332 IDEALS AND RATIONAL ACTIONS 

corresponding ideational elements, seldom occur separately 
in adult mental life; they combine to form mental states which 
vary tremendously in complexity. For convenience these 
states are classed as primary and secondary, according as they 
involve one kind of data or more than one kind. The relation 
of the mental states to their elementary data was shown in 
Table XIII (p. 231). 

Perception is the most important of the primary states 
(ch, xii) ; imagery is more important than feeling or conation 
(ch. xiii). 

Of the secondary states, emotions are the most primitive. 
They rest upon ancestral conditions, and in many cases prove 
a hindrance to the adjustment of response to stimulation under 
present conditions of life. Sentiments are the least important 
type. Volitions constitute a distinct advance in mental or- 
ganization (ch. xiv). Thought and language (and ideals and 
rational actions, which develop out of them) are the most mod- 
ern types of mental states and are by far the most impor- 
tant factors in mental life. They depend essentially upon 
social interaction of individuals and are peculiarly suited to 
bring about adjustment between the individual and his total 
environment. These types are still in course of active de- 
velopment in the human species. Rational thought, a special 
variety, is the most important single phase of mental life that 
has evolved up to the present (ch. xv). 

Physiologically, the formation of mental states is due to 
the summation of impulses in the cortical centers and the 
modification which this summation entails. In subjective 
terms, this is observed as a process of combining sensations 
(and ideas) into a single experience, which is transformed 
qualitatively in the process of combination. Retention, meta- 
bolic change, and distribution of impulses also enter into the 
central process, and are observed as revival, vividness, and 
discrimination of mental states. 



SUMMARY OF MENTAL STATES 333 

The development of specific mental states is due to the 
cooperation of three general factors: (1) Complex inherited 
cortical structure; (2) Specific forces in the general environ- 
ment, which act upon the given individual; (3) The social 
environment. The part played by social stimuli in molding 
mental states differs so widely from the influence of the gen- 
eral environment that the two may properly be treated as 
distinct factors. 

Collateral Reading: 
Stout, G. F., Analytic Psychology, ch. 10. 
Judd, C. H., Psychology, General Introduction (2d ed.), ch. 10. 
Titchener, E. B., Experimental Psychology of the Thought Processes, 

chs. 4, 5. 
Titchener, E. B., Text-Book of Psychology, sees. 139-147. 
Angell, J. R., Psychology, chs. 10, 11. 
Breese, B. B., Psychology, chs. 13-14. 
Urban, W. M., Valuation, chs. 2-5. 
Stout, G. P., Manual of Psychology, Book IV, ch. 5. 
Calkins, M. W., First Book in Psychology, chs. 9, 10. 
Stoerring, G., Mental Pathology in its Relation to Normal Psychology 

(trans.), chs. 9-11. 
Wundt, W., Volkerpsychologie, Vol. I, Die Sprache. 
Dittrich, O., Die Probleme der Sprachpsychologie. 
Muller, Max, The Science of Thought. 
London, J., Before Adam (especially ch. 4). 

Practical Exercises: 

What constitutes your thought of university, idiot, symphony, Egypt, 
steamboat, doxology, medicine, penitence? 

Ask someone to read aloud, and at the same time to think of other 
things; note how far his distraction interferes with pronunciation and 
especially with the inflections of voice which "give the sense." 

Examine how some ideal influences your plans of life. 



CHAPTER XVI 

SUCCESSION OF MENTAL STATES 

The Stream of Conscious Experiences. — In the four pre- 
ceding chapters we have examined the various types of men- 
tal states. Mental life consists of a succession of these states. 
One, neural process is followed by another, or in passing from 
center to center it undergoes modification so that the mental 
state is virtually transformed. 

The rise of a new mental state is due to the occurrence of 
some new stimulus. When we are reading and a loud noise 
occurs, the visual perception and thought give place to audi- 
tory perception. The transformation of mental states oc- 
curs when the impulse, in passing from one neuron to another, 
is modified by the condition of the second neuron. This is ob- 
served in a train of thought, where the word ' pyramid ' sug- 
gests the great pyramid of Egypt, this in turn suggests the 
Nile, and so on. 

The succession or flow of experiences in mental life has been 
aptly called by James the stream of consciousness. In inves- 
tigating this ' stream ' we should bear in mind that it is also 
a stream of neural impulses. In fact, the causal explanation 
of the succession and transformation of experiences from mo- 
ment to moment may be said to rest upon the physical and 
chemical properties of nerve. 

The psychologists of the 18th and early 19th centuries, par- 
ticularly those of the English school, formulated certain laws 
of the succession of thought. This succession they termed 
" association of ideas." They made little effort, however, 
to connect these laws up with the laws of neural activity.^ A 

^ David Hartley attempted this, but his treatment was based upon a crude 
conception of neural operation and was abandoned by later writers. The 
English associationists based their explanation of mental life almost wholly 



THE STREAM OF CONSCIOUS EXPERIENCES 335 

more serious defect in their work from the standpoint of sub- 
jective observation is that it ignores almost entirely the suc- 
cession of perceptions, feelings, and conative experiences 
which play an important role in mental life. 

The succession of ideational states (memories, general im- 
ages, fancies, thoughts) depends almost entirely upon central 
transformation of impulses. Succession of perceptions de- 
pends largely upon change of external stimuli. These consti- 
tute essentially different types of successions. But in actual 
life our ideational experiences are frequently broken in upon 
by perceptions and other sensory experiences ; our perceptions 
are often supplanted by ideas or are transformed by idea- 
tional accompaniments. Hence, the general succession of 
experiences in our mental life includes both types. We shall 
examine first the succession of perceptions and other sen- 
sory data, then the succession of ideational experiences, and 
finally the general succession of experiences in mental life. 

Stream of Perception. — A large part of our mental life 
is the direct result of external stimulation. This stream of 
perception depends primarily upon conditions in the environ- 
ment. The stimuli which affect our eyes, ears, skin, semi- 
circular canals, nostrils, etc., are due mainly to forces outside 
of our own body,^ which are for the most part independent of 
our mental processes. As a result, we do not control the flow 
of perceptions in the same way that we control our feelings, 
movements, and ideas. 

By closing the eyes we can remove most of our visual per- 
ceptions; we can turn the head and alter them. We can re- 
duce the intensity of an auditory impression by stopping the 
ears. A slight movement may serve to get rid of a sensation 

upon the association process. Their attempt to build up a complete psy- 
chology upon the laws of association was extremely useful in that it led to 
careful psychological analysis. But the theory was one-sided. There are 
many other mental operations besides suggestion. 

' The eye is also stimulated by the retinal circulation; a vascular stimulus 
gives 'buzzing' in the ears. These internal stimuli have usually little effect 



336 SUCCESSION OF MENTAL STATES 

of touch, warmth, or cold. By locomotion we are sometimes 
able to alter our entire external environment. But even these 
changes are only partly under neural control. When we 
move from one environment to another the actual stimuli are 
as much beyond our control as before. 

In other words, we are not able to mold and control percep- 
tion as we mold and control other types of experience. I can 
readily arouse the image or thought of my brother; but I can- 
not arouse a perception of him if he happens to be a hundred 
miles away. I can arouse the image of a rose and the feeling 
of pleasure at its form and odor; but I am unable to bring 
about a perception of its form or a sensation of its odor if 
there is no rose present in the environment to stimulate my 
receptors. 

Our control of perception, then, is largely inhibitory in char- 
acter. We can reduce a perception to the margin of conscious- 
ness by attending to some other experience or by closing the 
eyes, walking away, etc. Or we can modify a perception by 
adding images or thoughts to the experience. But we have 
little power to produce a stated perception at any time. The 
ultimate source of perception lies in the world outside of us. 

The chief role of the nervous mechanism in connection with 
the succession of perceptions is (1) to focalize some percep- 
tions and render others marginal, and (2) to select from 
among a number of possible perceptions by means of motor 
activity. 

Generally the perceptions which are focalized or selected 
are those that serve our purposes and ideals in life. The 
growth of central control depends upon two factors: (1) learn- 
ing to distinguish certain kinds of stimuli, and (2) the fitness 
of certain stimuli to nourish us, protect us, and adjust our 
relations with the environment. Given two individuals in the 
same general environment and subject to practically the same 
external forces, one perceives one set of objects and events, 
the other may perceive quite a different set. A great number 



STREAM OF PERCEPTION 337 

of people were passing the corner of Broadway and Wall Street 
at 11 o'clock last Thursday. All were subject to practically 
the same external conditions, but if they were asked to state 
what they saw, heard, and experienced generally, their reports 
would show tremendous differences. The newsboy watches 
to see what faces are attracted by his cries and the headlines, 
and what hands reach into the owTier's pocket. The farmer 
notices the fruit stands and the horses. The broker's clerk ob- 
serves shreds of ticker tape and certain buildings which he is 
accustomed to visit. The student of psychology is impressed 
with the throng of people and studies the expression of their 
faces. The beggar is on the lookout for very different expres- 
sive signs. In a word, from the total mass of stimuli which 
affect our external receptors at any time, we pick out certain 
kinds which- have become familiar through repetition and 
which fall in with our life interests. 

Laws of Perceptual Succession. — The role of the two fac- 
tors, external stimuli and neural functions, in the succession 
of perceptions may be stated in the following laws: 

(1) The succession of perceptions depends primarily upon 
changes of external stimuli. 

(2) It depends upon the maimer and conditions of stimu- 
lation. The same visual stimulus produces a different effect 
(i.e., the perception is altered) according as it strikes the 
center of the eye, the periphery, or the back of the head.^ 

(3) It depends upon the retention effect of previous similar 
stimuli. Repetition and retention improve one's ability to 
pick out certain stimuli and combine them into perceptual 
states. 

(4) It depends upon present metabolic conditions. These 
result in inhibiting certain perceptions, focalizing others, and 
retaining others in the margin. 

(5) It depends upon kinesthetic stimuli. Motor activity 
enables us to get rid of certain stimuli and substitute others — 

^ In the last case it does not serve as stimulus at all. 



338 SUCCESSION OF MENTAL STATES 

as when we leave the city for the country or attend a concert 
to hear a certain piece of music. 

The succession of perceptual experiences depends upon 
these five conditions. All but the first are functions of the 
receptors and of the nervous system. 

Stream of Thought. — The adult mental life of civilized 
man often includes a long succession of ideational states un- 
interrupted by perceptions. Perceptual elements as. well 
as systemic and kinesthetic may appear among the com- 
ponents, but the dominant character of the state is ideational 
— either some sort of imagery, or a thought. The starting 
point of such a series is always a perception or some other 
type of sensory experience, but the train of ideas, once 
started, may proceed for a long time without interference by 
sensory states. 

Iq subhuman species prolonged trains of ideas apparently 
do not occur. If an animal experiences a memory image or 
an image of any sort, this mental state either leads directly 
to motor expression, or it is immediately succeeded by some 
new perceptual experience. 

A dog gives evidence of remembering his master after pro- 
longed absence, but instead of this memory starting a train 
of reminiscences, it leads at once to barking, frisking about, 
and vigorous wagging of the tail. Even while the memory 
image lasts it may be interrupted by a word or gesture 
from his master which introduces a new sensory expe- 
rience. In lower animals the image life is even more frag- 
mentary. 

In man the image life, and more especially its higher form 
the thought life, tends to become one of the most important 
phases of mental life. A perception arouses a thought, this 
thought excites another thought, this in turn a third, and so 
on. Thus a long series of thoughts may arise in quick suc- 
cession, each independent of external stimulation except at 
the very beginning. 



LAWS OF IDEATIONAL SUCCESSION 339 

Laws of Ideational Succession. — The succession of idea- 
tional processes (imagery and thought) is usually called as- 
sociation of ideas. Psychologists early discovered certain uni- 
formities in the mode of succession, which were formulated 
as " laws of association," or laws of suggestion. These uni- 
formities were first noted by Aristotle, who is responsible for 
the laws of contiguity, resemblance, and contrast. Hartley, 
James Mill, and their followers elaborated the laws, but 
rejected contrast as an independent mode. 

The recognition of the laws of association in thought is of 
practical importance, since the average man is inclined to 
regard the succession of his thoughts as due to mere chance 
or mere volition. At times we seem to create new thoughts 
quite arbitrarily and with no reference whatever to previous 
experiences. We see no reason except pure chance why oui 
thought of a trip to the city should be succeeded by the 
thought of John Bunyan. Or we attribute the connection 
to some subconscious force or underlying personaUty. 

Actually, the succession of thoughts is due to the opening 
up of synaptic connections between neurons, and probably 
also to modal changes in the nerve impulse as it passes from 
one central neuron to another. Apart from the intervention 
of sensory elements during the process, the succession of 
ideational states depends wholly upon the past and present 
condition of our nervous system. 

The neural process specially characteristic of succession is 
conduction (ch. iv); the corresponding conscious process is 
suggestion. The laws of ideational succession may be stated 
either as laws of associative suggestion or as laws of neural 
processes.^ 

(1) Law of Similarity: A perception or idea tends to sug- 
gest a similar idea. — When we see a stranger we tend to 
think of a friend whom he resembles; or again, the thought 

■ The neural interpretation of these laws is stilly a matter of theory. See 
Appendix, "Neural Activity," p. 435. 



340 SUCCESSION OF MENTAL STATES 

of Mr. Tubbs may lead us to think of Mr. Hubbs because the 
two names are similar in sound. The thought of Caesar leads 
many to think of Alexander or Napoleon, because the careers 
of these three men bear many resemblances to one another. 
— Stated in neural terms, an impulse in one neuron tends 
to pass over into another neuron which has been similarly 
excited. 

(2) Law of Contiguity: A perception or idea tends to 
suggest another idea which was previously experienced near 
it in space and time. — When we hear the opening strains of 
the Lohengrin Wedding March the perception arouses the 
image of the following tones; the thought of sunset may 
arouse the thought of night. Or again, the thought of a cup 
may lead to the thought of the saucer; the memory of a house 
may bring up the memory of a certain room. In the first two 
instances the contiguity is temporal, in the last two it is 
spatial. — In neural terms, when a complex impulse passes 
into a neuron whose trace is partly similar in mode it tends 
to be modified by the non-similar features of the retention 
trace of that neuron. This means that when the impulse 
passes into the second neuron it tends to become more like 
the previous impulses which affected that neuron. 

The laws of similarity and contiguity may be combined. 
The similarity between two ideas or two objective things 
means that they are partly congruent and partly different. 
Suggestion means that when the * same ' elements recur in 
thought they lead to the reinstatement of accompanying 
dissimilar elements. But the unlike elements are reinstated 
through contiguity. For example, I think of the World War, 
and this leads to the thought of the peace of Westphalia. 
Certain elements in the idea of war are the same for any war; 
to these identical elements are attached contiguous experi- 
ences which are dissimilar in the two cases. The identical 
elements in the two experiences lead to the reinstatement of 
certain dissimilar elements present in the earlier experience. 



LAWS OF IDEATIONAL SUCCESSION 341 

This Law of Reinstatement may be expressed as follows : 
A mental state tends to reinstate a previous mental state, 
part of whose constituents are congruent with the former. 

It is obvious from this that one idea may lead to a number 
of different associations. The word ' beware ' sometimes 
suggests ' pickpockets,' sometimes ' a widow.' Just which 
one of these actually follows depends upon other conditions, 
which are expressed in other laws of association. 

(3) Law of Frequency: An experience which has been 
repeated many times tends to be suggested in form of a 
memory or thought more readily than an experience which 
has occurred in the past only once or a few times. — We re- 
call the name or looks of a friend much more readily than we 
recall a stranger. The same phenomenon appears in language; 
we recall and repeat far more readily phrases which we have 
memorized than those which we have read or listened to a 
few times only. — In neural terms, repetition improves the 
synaptic connections between neurons and thus facilitates 
the future passage of an impulse along the same path. 

(4) Law of Vividness: Among alternative ideas which 
might follow a certain mental state, that idea tends to be 
suggested which was more intense or vivid when it occurred 
previously as a perception or thought. — We tend to recall 
more readily an important event or thrilling experience 
which we have undergone; we are most apt to recall vivid 
pictures and clean-cut phrases. — In neural terms, an in- 
tense impulse tends to modify in a marked degree the 
neurons through which it passes, and this renders it more 
likely to affect future experiences. 

(5) Law of Recency: A recent experience tends to be sug- 
gested as a memory or thought more readily than an ex- 
perience which occurred some time ago and has not been 
repeated meantime. — We recall, for example, many more 
experiences of the past week than events which occurred 
during some week a year or ten years ago. — In neural terms, 



342 SUCCESSION OF MENTAL STATES 

a synaptic connection which has been recently used is more 
permeable than a path which has not been used for a long 
period of time. Connections in the central nervous system 
tend to become resistant through disuse. 

The factors oi frequency, vividness, and recency interact and 
modify one another's effects. Thus a vivid experience which 
occurred many years ago may be suggested more readily than 
a recent experience of lesser vividness. Frequent repetition 
may strengthen a remote experience, or on the other hand 
an experience which has not been attended to or focalized 
may not be recalled even though it has been repeated many 
times. It is diflScuIt for us to memorize a set of instructions 
on a subject which possesses no interest, no matter how many 
times we rehearse them. 

Classes of Associations. — Experimental psychology has 
investigated the strength of various sorts of relationship in 
producing suggestion. In addition to spatial contiguity, 
temporal contiguity, objective similarity, verbal similarity, and 
contrast, the general image and symbolic thought introduce 
certain logical relationships. These include coordination (of 
two general ideas of species belonging to the same genus, such 
as red — yellow, both being colors), subordination (table — 
leg, vertebrate — man), cause and effect (fire — heat), means 
to an end (listen — hear) . Investigators have examined, 
among other problems, the comparative frequency with 
which different sorts of relationship occur in association and 
the comparative length of time required to form an associa- 
tion of each sort. [Table XVIII.] 

Control and Limitations of the Thought Series. — The suc- 
cession of thoughts is to some extent subject to personal 
control. Repeated experiences of the same general sort 
build up not only general images and thoughts, but attitudes 
(ch. xvii), which determine the direction of the stream of 
thought. In addition, a dominant thought may persist 
during a long period, and may form a ' core ' or nucleus 



CLASSES OF ASSOCIATIONS 



343 



Table XVIII. — Classes of Associations 



Frequency 



Time {a) 





Percent 


Aud. Stim. 


Vis. Stim 


Verbal 


27.89 


2083 


1972 


Auditory or visual similarity 


4.05 


2088 


2425 


Completion of words 


23.84 


2082 


1866 


Meaning 


59.82 


1949 


1992 


Perceptual relations (5.61%): 








Spatial and whole-part relations 


3.86 


1851 


1811 


Temporal relations 


1.75 


1847 


1801 


Conceptual relations (31.45%): 








Contrast 


9.45 


1356 


1752 


Similarity 


4.03 


1543 


2017 


Synonym 


5.57 


1819 


1728 


Subordination 


1.12 


1780 


1621 


Specification 


1.12 


2513 


1979 


Cause 


2.21 


2044 


2333 


Effect 


2.37 


1884 


1799 


Other relations 


5.58 


1649 


1761 


Connections (22.76%) : . . 








Spatial or temporal connections 


3.83 


2613 


2094 


Predication 


18.93 


2301 


2363 


Manifold relations 


8.36 


1796 


1853 


Mediated associations 


2.21 


1996 


2146 


Unidentified 


1.72 


2247 


1824 



Relative frequency of various types of association and time required to 
form them (in sigma, lOOOths of second) when the stimulus word was pre- 
sented auditorially (22 subjects) and visually (3 subjects). Total stimuli: 
6162 auditory, 630 visual. [From A. Wreschner, Die Reproduktion und As- 
soziation von Vorstellungen, pp. 261-2. The classes have been consolidated 
in some cases and the general classes renamed.] 



around which other thoughts are successively gathered. 
Such a dominant idea may produce a general ' set,' which 
controls the direction of our thinking at some future time. 
We impress upon ourselves the thought of an important en- 
gagement at 5 o'clock. The thought passes, but at 5 o'clock 
recollection occurs — in most cases ; not always, alas. These 
central impressions are often assisted by external cues; we tie 
a string around the finger or hide a stocking before going to 
bed. More effectively, we enter a note on a memorandum 



344 SUCCESSION OF MENTAL STATES 

or place an empty cigar box inside our hat. All such mental 
and physical operations are systematic adaptations which 
form part of the general function of central control. They 
involve the processes of successive thinking, whose workings 
are formulated in the laws of suggestion. 
A train of thought once started continues indefinitely. 

(1) It may be checked by some strong sensory stimulus, 
which produces a vivid sensation .and thereby reduces the 
ideational state to the margin. We are aroused from thought 
by hearing someone call or by the presence of some new ob- 
ject in the field of vision. 

(2) A train of thought may be checked by the discharge of 
the nerve impulse into a motor pathway, resulting in motor 
activity. The sudden thought that it is time to attend a 
lecture ends our reverie, if the thought passes into immediate 
action. 

(3) Swooning, sleep, and hypnosis may inhibit thought or 
impede its progress. In a swoon or coma the central process 
is reduced to a minimum intensity or disappears entirely. 
Sleep and hypnosis do not affect the thought processes so 
profoundly as they affect sensations. In sleep, sensory 
stimuli are generally ineffective; sensation is greatly reduced, 
but in many cases trains of imagery and thoughts take place. 
In hypnosis sensations are largely marginal, and ideational 
states are dominant; the flow of thought is controlled to an 
unusual degree by verbal stimuli. 

Sleep and Dreams. — Sleep is an important factor in our 
vital life. In man it covers about one- third of the entire 
day and is an essential part of the organic repair process. 
The period of sleep enables the organism to restore the 
material used up by the activities of waking life. Anabolic 
processes predominate during the sleep period. As a physi- 
ological condition, sleep is just as normal as waking life, but 
the mental processes {dreams) which occur during sleep 
present many unusual if not abnormal features. 



SLEEP AND DREAMS 345 

During sleep the central nervous activity is greatly re- 
duced in intensity, though in many cases it is still sufficiently 
intense to be focal. . The distinctive fact in dream states is 
that the central neurons are almost wholly cut off from their 
sensory and motor connections. The synapses which join 
the sensory paths with the brain and the brain with the 
motor paths become highly resistant. Only intense sensory 
impulses penetrate to the higher centers, or impulses which 
play a prominent part in our mental life. On the other side 
of the arc, motor discharge is checked, so that an idea which 
in waking life would lead to speech,.locomotion, or some other 
coordinated activity either remains without any motor ex- 
pression, or at most produces a rudimentary effect. 

During sleep we are not centrally affected by ordinary 
sounds, lights, odors, etc. A very loud sound may penetrate 
to the centers and arouse us; or a sound which possesses un- 
usual personal interest, as when the child's fretting wakens 
the mother. Organic stimuli are often very effective; the 
unpleasant and terrifying dreams known as nightmares 
are attributable to indigestion. Temperature stimuli suggest 
dreams of a conflagration or of walking the streets unclad. 
Tactile stimuli are rarely effective. 

On the motor side the autonomic processes proceed much 
as in life. The breathing is more regular and may take on a 
new rhythm. Occasionally a strong motor impulse breaks 
down the resistance, as when we turn over in bed or talk in 
our sleep. Sleep-walking occurs when specially strong mo- 
tor impulses find effective expression without wakening the 
sleeper. The very beginning of such movements serves to 
waken most persons, but in certain individuals and under 
certain conditions somnambulism proceeds in a coordinated 
manner. The same is true of sleep-talking. Where the 
motor impulse does not produce actual movement, it is 
found in many cases that slight twitching movements of 
the feet, arms, fingers, and throat occur. These incipient 



346 SUCCESSION OF MENTAL STATED 

movements are probably more common than is generally 
supposed. 

There is usually no indication to an .outside observer that 
any memory or thought process is taking place, and the 
sleeper himself may recall nothing on waking. This negative 
evidence is not conclusive proof that the higher centers are 
quiescent; for the connection between sleeping thoughts and 
waking thoughts is often very slender, and we frequently re- 
call a dream immediately after waking only to lose all recol- 
lection of it soon after. Accordingly, when one declares that 
he never dreams we can only infer that he is unable to recall 
dreams. On the other hand, the fact that many dreams are 
forgotten does not justify the sweeping conclusion that we 
always dream during sleep. Certain of the higher centers are 
quiescent at one time or another, and it may be that for some 
sleepers every higher center is at rest. 

Dream experience differs from waking experience princi- 
pally in that the central field is narrowed; certain central areas 
are cut oflf from the sensory and motor pathways. This seems 
sufficient to explain the fantastic character of dreams and the 
absurdities which they exhibit. Since our brain centers are 
largely cut off from sensory impulses, their activities consist 
chiefly of imagery and thoughts. Dream images may not be 
actually more intense than the imagery of waking life; but 
since there are no sensations with which to compare them 
they become for the time being the most intense and vivid 
mental states we are experiencing. When I picture a book 
or a man in waking life the image shares the field of conscious 
experience with many perceptions. Compared with these it 
is far less intense and is usually less vivid. In dream life the 
book or the man appears to be actually before us. 

Again, in dreams events proceed in most absurd and incon- 
sequent fashion. I take a party of friends out motoring; an 
instant later we are gliding along through a narrow canal. I 
leap to the bank and ascend a hill in company with my grand- 



SLEEP AND DREAMS 347 

father, who has been dead some thirty years. I leave him 
for a moment to make sure of the road, and on returning he 
has disappeared and is nowhere to be found. As perceptions 
of external phenomena this train of experiences involves a 
tissue of absurdities; but one may find its counterpart in 
many a train of thought which takes place during waking 
life. 

Dream experiences may contradict our knowledge of phys- 
ics and other natural laws, as when we dream of walking on 
air. One dreams of reading in the paper an account of a foot- 
ball game and at the same time he is rushing down the field 
with the ball under his arm. In waking life this is paralleled 
when we read of an event and at the same time form images 
of what we read about. The difference is that in dreams we 
have no external data to compare with the ideational states, 
and the latter attain the vividness of perceptions. We dream 
of Africa and we find ourselves there. We dream of a dead 
friend and he stands before us. 

Since in sleep many of the centers are cut off from one an- 
other, we are often unable to associate the given experience 
with our built-up store of memories. Thus we find nothing 
startling or unreal in seeing before us someone long dead. At 
times an incongruity may be noticed and may puzzle us, as 
when we discover one family living in a house which we know 
is occupied by another. In such cases a false memory may be 
constructed to explain the contradiction ; we ' recall ' that 
A rented or sold the house to B. These false memories are 
counterparts of the thoughts which arise when we seek to 
account for apparent contradictions in waking life. In 
waking life we say, " Did A rent or sell the house to B? " 
In dreams the thought takes on the character of a memory 
image. The sudden appearance and disappearance of objects 
and persons in dreams is an indication that the apparently 
perceptual states are thoughts; dream experiences ' behave ' 
like ideas, not like external things. In every respect dreams 



348 SUCCESSION OF MENTAL STATES 

proceed in the same way as trains of thoughts, and not as 
trains of perceptions. 

Since dream states are thoughts, and not voluntary acts, it 
is readily understood why honorable persons sometimes dream 
of committing dishonorable actions, such as lying, stealing, 
or killing. Everyone thinks of these acts, though in waking 
life we usually think of them as performed by someone else. 
In dreams, experience tends to a more subjective form. When 
we dream of the act of stabbing, the kinesthetic part of the 
experience is more vivid than in waking thoughts, and the 
mental state reproduces the central conditions of volition, 
without the motor activity. We picture ourselves as perform- 
ing the act. 

The Freudian psychology emphasizes the importance of our 
subconscious life in determining dreams. According to this 
view, in waking life certain thoughts which distress us or 
render us uncomfortable are banished from the focus of con- 
sciousness and even from the ' margin ' as that term is gener- 
ally understood. They still persist, however, in subordinate 
centers, and constitute an underlying part of mental life, 
called the subconscious. The subconscious part of our mental 
life inhibits motor impulses aroused by conscious states and 
sends out motor impulses of its own. According to Freud 
the activity of the subconscious self is shown in many of our 
defensive reactions, and in our endeavors to conceal our true 
personality from others; it is betrayed by certain unaccount- 
able acts on our part, by slips of the tongue or pen, and by the 
phenomena which accompany hysteria. Dream life is inter- 
preted by Freud as a conscious manifestation of the subcon- 
scious self; the subconscious rises to the level of conscious 
experience. 

Our study of dream phenomena in this section indicates 
that they proceed in precisely the same way as other trains of 
ideas. The " marginal mental life," with its manifold asso- 
ciated connections, often determines the trend of thought in 



SLEEP AND DREAMS 349 

waking life. It probably determines the flow of dream ex- 
periences to the same extent. But the facts do not seem to 
require the hypothesis of an organized subconscious person- 
ality in the Freudian sense in order to account for the phe- 
nomena of dream life. 

Hypnosis and Hypnotic Suggestion. — Another special con- 
dition of nervous organization is hypnosis. In this state the 
sensory and motor paths are not entirely cut off as in sleep, 
but certain pathways become more resistant, while others 
are unusually open to connection with the centers. The phys- 
iological state of hypnosis includes several phases, such as 
catalepsy, lethargy (trance), and somnambulance. 

Psychological interest attaches especially to the peculiar 
suggestibility which appears in hypnosis. Verbal stimuli be- 
come much more effective than in waking life. The hyp- 
notized ' subject ' is directed to perform an act and he does it 
unquestioningly. If told that he is in a lake he immediately 
begins to make swimming movements. If it is stated that a 
sheet of blank paper is a letter from a friend he starts to read 
it. Suggestion may induce anesthesia of one or more of the 
senses. The subject will not flinch when pricked by a needle 
or touched with a hot iron, if the proper command be given. 
Hypnosis is characterized at times by hyperesthesia of one 
of the senses; the subject is able to distinguish one blank sheet 
from another when told that they are photographs of differ- 
ent people. The ordinary sense of proportion and fitness 
may be quite lacking in hypnosis, and one will unhesitat- 
ingly perform acts which ordinarily would be inhibited by 
the feeling of absurdity or fear of ridicule. 

The mental state during hypnosis is a condition in which 
the thought-life is raised to the focus, and perceptions and 
other sensations become less vivid. The succession of men- 
tal states in hypnosis follows the laws of ideational suggestion 
rather than the perceptual laws; but the stream of thoughts 
is controlled by verbal stimuli received through the external 



350 SUCCESSION OF MENTAL STATES 

senses. These stimuli are communications; they are social 
in character. 

Social suggestion is an important factor in normal life. To 
a certain extent everyone is influenced by the words and 
acts of those about him. But in normal life the individual's 
personality, molded by past experiences, inhibits to a large 
extent the effect of such suggestions. In hypnotic life these 
inhibitions are lacking, and the suggestions received from the 
hypnotizer govern the flow of experiences. Only when they 
conflict with the most fundamental principles of our moral 
life do they seem capable of arousing resistance. 

Reasoning. — Reasoning, or rational thinking,^ is a special 
variety of trains of thought. It is distinguished from ordi- 
nary successions in that it is based largely upon meanings 
and values. 

Our thoughts and images depend upon the retention trace 
left in our neurons by past perceptual experiences. But exter- 
nal stimuli affect us in haphazard order, so that the succes- 
sion of perceptions is often quite unsystematic. The casual 
relations among perceptual experiences tend to be reproduced 
in OUT trains of thought. Thus our ordinary trains of thought 
may bring into association objects or events which are not 
actually connected in nature. I think of the former head of 
Princeton, James McCosh, and I think of the king of Eng- 
land; associating the two thoughts together I think of James 
McCosh as King of England. There is no more neural diffi- 
culty in making this connection than in associating the thought 
of another head of Princeton, Woodrow Wilson, with the 
thought of the presidency of the United States. But in the 
latter case the thought train corresponds to objective facts, 
in the former case it does not. 

Reasoning is a special form of ideational succession which 
follows the processes of nature, and hence if the first state in 
the series corresponds to objects or relations in the exter- 
^ Thinking involves a succession of thoughts. 



REASONING 551 

nal environment the train will represent objective facts and 
relations or changes. For example, 27 + 14 = 41 is rational 
thinking. If we think of fourteen dollars added to twenty- 
seven dollars we conclude that there will be forty-one dollars 
in the group. The final thought of the series tallies with ex- 
ternal conditions because the mental train is based upon ex- 
ternal relations. The same applies to sheep or beans or 
bottles or anything else. We may reason about objects such 
as mermaids or philosopher's stones which do not exist in 
the external environment; or we may reason about relations 
which we have not observed in nature, such as negative and 
imaginary numbers or curved space, provided they fit in with 
observed relations. On the other hand the association of re- 
lations which contradict external experience is not rational 
thinking. We can perfectly well think 27+14 = 39; but this 
is not a rational train of thought — it contradicts all our ex- 
periences of relations in the external world. 

The rational type of association has been built up through 
our dependence upon the external world for the satisfaction 
of oxu" wants and desires.^ The association 27 + 14 = 41 
tallies with our perceptual experiences time and time again; 
hence it has an advantage over the association 27+14 = 39 
or other alternatives, which occur casually and rarely, which 
have no counterpart in perceived relations, and which do not 
serve to satisfy our needs in practical situations. 

The fundamental principles of mathematics and logic give 
rise to certain fundamental modes of rational association. 
These fundamental modes are illustrated in rational trains of 
the form 

A = B and B = C; hence, A = C 
A>B and B>C; hence, A>C 

It is perfectly possible for us to form thought trains which 

flatly contradict these logical principles. We can think of 

1 These are mental attitudes which will be discussed in chapter xvii. 



35^ SUCCESSION OF MENTAL STATES 

John as taller than Henry, and Henry as taller than William, 
and William as taller than John. But when we test this out 
with actual external relations we find that it fails to meet 
the test : the third member of the thought train does not cor- 
respond to external facts. 

Another mode of rational thinking consists in following out 
in detail the steps in a series of events. In ordinary sequences 
of thought I think of going from New York to Chicago, 
and immediately after I may think of my arrival there. In 
rational thinking I first consider the manner of getting to 
Chicago, think of consulting the time-table, packing, driving 
to the station, purchasing my ticket, and boarding the train. 

The psychological characteristic of rational trains of 
thought is the vividness of the meaning and value elements in 
its members. This differentiates rational from casual think- 
ing. When I think rationally of going to Chicago, the image 
elements corresponding to actual external conditions are 
vivid; the idea is not merely the arbitrary name Chicago, but 
imagery of actual perceptual situations which I might ex- 
perience in getting there. The image elements in thought 
which correspond to perception constitute its meaning factor 
(ch. xv). In the same way quantitative reasoning (mathe- 
matics) is due to the vividness of the value elements in thought. 
When I add up a column of figures by mere casual association 
the value elements are marginal, and I frequently reach dis- 
cordant results. When the value elements are focal the re- 
sult is uniformly the same and tallies with external relations. 

In the mental life of subhuman animals perceptions and 
other sensory types of experience are predominant; the 
ideational side is rudimentary. Hence, their actions, in- 
stinctively determined, tend generally to haTmonize with 
nature. It is only when thought life begins to be predom- 
inant that disparity arises to any extent between the environ- 
ment and organized reception. When reasoning is in the 
first stages of development it results in a host of irrational 



REASONING 353 

conclusions; these form the basis of superstition, magic, and 
mysticism. Gradually rational thinking becomes differ- 
entiated from casual thinking, and as a result the mental life 
of civilized man is vastly more in harmony with the external 
world than the mental life of his primitive ancestors. 

Among civilized races irrational thinking persists in dream 
life. In dreams our trains of thought sometimes follow the 
rational pattern, but more frequently they belong to the 
casual type. The dreamer lacks perceptual checks and a 
background of memory, and is unable to harmonize his judg- 
ments with actual conditions of the environment. 

In many types of mental disorder the irrational pattern 
predominates. Perceptual tests are present, but the central 
connections are out of gear; the normal relations of sensation 
to thought and memory are distorted. Hence, among the 
insane either the whole system of thinking is irrational ; or in 
some cases a fine, well-balanced train of reasoning is utterly 
vitiated by a single irrational step which the subject is unable 
to rectify. A certain patient would be a successful contractor 
and builder if he did not spend most of his time in devising 
means to rid himself of the electricity with which he declares 
* they ' have filled his head. 

In normal waking life the principles of reasoning are con- 
stantly used in our trains of thinking. We do not focalize 
these principles specifically, but our thoughts nevertheless 
follow one another in a rational manner. Occasionally in the 
midst of rational thinking a casual association slips in. When 
we are adding a colmnn of figures our thoughts of 8 and 7 may 
be followed by 13; or in a chess game we may think of moving 
a certain piece and afterwards think of it as still occupying 
the former square. Such slips are common with everyone, 
but a careful thinker is likely to discover and correct the 
error by noting some inconsistency to which it leads. 

The evolution of rational thinking (reasoning) is the most 
important step in the growth of adaptive behavior. It en- 



354 SUCCESSION OF MENTAL STATES 

ables us to anticipate occurrences in the environment and 
prepare for them. Non-rational thinking cooperates with 
it ordinarily. By combined rational and casual thinking we 
imagine situations more or less contrary to actual experience, 
and consider how we would act in such circumstances. The 
harmonizing of our actions with the conditions of the envi- 
ronment is brought about most effectively by this cooperation 
of the two types. 

General Stream of Experiences. — The stream of experi- 
ences which make up mental life in its entirety includes data 
of every sort — perceptions, imagery, feelings, conations, 
emotions, sentiments, volitions, thoughts, and ideals. These 
follow one another in various ways. With the exception of 
perceptions and thoughts we rarely experience a long train 
of one single kind of mental state. Usually a feeling leads 
to some sort of expression, which transforms the feeling into 
a conation or an emotion. Conative experience leads to new 
perceptions or to thought. An emotion soon exhausts itself 
and gives place to some other type of experience; while a 
volition results in motor activity, which is followed by a 
brand-new set of external stimuli. 

With respect to their mode of transformation mental 
states may be grouped into three classes: (1) those which 
depend mainly upon conditions outside the organism; (2) 
those which depend upon internal stimuli; (3) those which 
are equally dependent upon external and internal conditions. 

Perceptions belong to the first class, thoughts to the 
second; the other types of mental states depend upon both 
external and internal conditions and consequently follow 
both sets of laws given above. An emotion may be modified 
by a change in the external surroundings, or it may be swept 
away or completely transformed by changes within our organ- 
ism. Our fear during a storm at sea may be intensified by 
the sound of a crash; or it may be transformed into awe when 
we think of the tremendous power of the waves. Our voh- 



GENERAL STREAM OF EXPERIENCES 355 

tion to go to the library disappears when we reach our des- 
tination; it may disappear sooner if we remember that the 
building is closed. 

Conscious mental life may be regarded as a succession of 
experiences of every sort, one leading to another of the same 
or of a different type. In the general vista of experience 
there may be long unbroken stretches of perceptions and 
long unbroken stretches of thought; between these, patches 
of other experiences are interspersed here and there. 

In almost every individual, civilized or savage, perceptions 
are most frequent and occupy the dominant position. Among 
educated adults of civilized communities ideational experi- 
ences occupy a good second place. Among primitive peo- 
ples the emotional life occupies a higher rank than thought 
and imagery. The expressive life (conation, volition, lan- 
guage) generally holds the third place in civilized races, com- 
ing ahead of the emotions; among savages it may also stand 
third, ranking just below the emotions; at times it may even 
occupy the second place. 

Our experience at any given instant is ordinarily complex — 
it may include several distinct components, such as percep- 
tion, thought, and volition. Where this occurs one of the 
states is usually focal and the others marginal. In the course 
of time some of the coexisting states are weakened and others 
strengthened by external or internal conditions; certain 
focal states fade into the background and certain marginal 
states become focal. If I observe my focal experiences and 
ignore the rest, my mental life appears to be constantly 
changing from thought to perception, and back to thought 
again — even apart from the changes produced by new 
stimuli. When I think about writing this chapter my per- 
ception of surrounding objects is marginal ; suddenly my eye 
falls upon a clock and I jump up and get my hat; then having 
set out to meet my appointment the train of thought is re- 
sumed. At first sight the train appears to have been broken 



356 SUCCESSION OF MENTAL STATES 

and then renewed. Close observation may show, however, that 
it was proceeding, at least marginally, during the second stage. 

Reaction Time. — The duration of experiences has been 
measured approximately in cases where reaction takes 
place immediately. If a stimulus gives rise to perception, 
recognition, etc., and a definite response follows at once, the 
period beginning with the stimulation and ending with the 
movement is called the reaction time. The central portion 
of this period is found by subtracting the sensory and motor 
conduction time from the total duration. Since the rate of 
nerve conduction is not known exactly, the duration of the 
mental state is subject to a certain error of calculation. But 
we can compare perception time with recognition time and 
association time provided the same receptor and effector are 
used, since the conduction time is the same in such cases. 

Reaction times are usually measured by a chronographic 
record of tuning fork vibrations, or by a chronoscope whose 
dial indicates lOOOths of a second (o"). When the stimulus is 
given the chronoscope is electrically started. The reaction 
is usually made by pressing a key which stops the chrono- 
scope hands. With the chronograph the beginning and end 
of the reaction are marked on the record. 

Visual reaction is found to be considerably longer than 
auditory or tactile — probably owing to a difference in the 
nature of the receptor processes. There is also a difference 
in reaction time according as the attention is fixed upon the 
stimulus (sensory reaction) or upon the movement (muscular 
reaction). While individuals differ considerably in their 
reaction time, numerous experiments indicate the following 
averages for simple perceptual reactions: 

Stimulus Sensory attention Muscular attention 
Light 2900- 1800- 

Sound 225 120 

Electric on skin 210 105 

[Prom Titchener, Text-Book, p. 432.] 



REACTION TIME 357 

Titchener found in his own case that recognition of a color 
required 28o" longer than simple sensory visual reaction. 
Recognition time for a letter of the alphabet was 51a- and for 
a short word 45a". These relative differences hold generally, 
though the absolute times vary; it requires less time to rec- 
ognize a word of three letters than a single letter. 

Many investigations have been made on other complex 
reactions, such as discriminating between sounds of different 
pitch, reacting with one finger for one sound (or color) and 
with a different finger for another, associating some idea 
with a stimulus word, etc. The association times of various 
sorts of relationships are shown in Table XVIII (p. 343). 

Laws of the Succession of Experiences. — The role of 
various factors in determining the general flow of experience 
may be expressed in the following laws : 

(1) The succession of experiences depends upon the relative 
strength of the nerve impulses which occur momentarily. 

(2) The initial strength of any impulse depends primarily 
upon the strength of stimulation. 

(3) The strength of an impulse is altered during its course 
by the momentary metabolic condition of the several synapses 
through which it passes ; this metabolism varies with local or 
general fatigue, rest, attention, distraction, etc. 

(4) The summation and distribution of impulses (subjec- 
tively observed as mental succession) depends primarily upon 
the structural arrangement of the neurons into a system, in- 
herited from our parents and modified by growth, use, and 
injury. 

(5) Motor impulses generate new stimuli, which may lead 
directly to new systemic or motor sensations and indirectly 
to new external sensations. 

(6) The strength of ideational impulses in transforming or 
overcoming sensory impulses depends upon the resistance of 
the retention set. 

By taking these several factors into account the tranS' 



358 SUCCESSION OF MENTAL STATES 

formation of one experience into another may be explained 
in concrete instances. In many cases the transition is not 
abrupt, but consists in a marked increase of vividness on the 
part of some mental state already marginally present, accom- 
panied by a decrease in vividness of the mental state which 
has hitherto been focal. The succession here is not so much 
a transformation as a readjustment of the relative strength of 
the several parts of the whole field of experience; it is com- 
monly known as 'change of attention.' 

The role of metabolic conditions (third law) may be tested 
by listening to a very faint sound — one which borders on the 
threshold of sensation. If we listen intently, with no dis- 
turbing stimuli of any sort, we hear the sound for a time, then 
lose it, then hear it again, etc. This phenomenon, generally 
called the 'fluctuation of attention,' indicates a rhythm in 
the physiological processes. 

The part played by heredity is indicated in the fourth law, 
and the influence of the environment in the second law and 
the latter part of the fourth. 

The last two laws indicate the role of the individual himself 
in controlling the succession of his own mental states. The 
fifth law shows how we initiate new experiences. The sixth 
emphasizes the importance of our past life and personality in 
directing our stream of mental states. Our mental back- 
ground includes something more than the specific effects of 
this and that concrete past experience. Retention traces 
modify one another and this results in general ideational 
modes or tendencies which influence the course of experience. 
A general trace of this sort is called an attitude. 



Collateral Reading: 
Breese, B. B., Psychology, ch. 12. . 

Titchener, E. B., Text-Book of Psychology, sees. 105-111. 
James, W., Psychology, ch. 16. 
Arnold, F., Psychology of Association. 
Calkins, M. W., Association, Psychol. Monog., No. 2. 



LAWS OF SUCCESSION OF EXPERIENCES 359 

Wreschner, A., Reproduktion und Assoziation von Vorstellungen, Zsch. f. 

Psychol., Ergbd. 3. 
Hartley, D., Observations on Man, Part I, chs. 1-4. 
Mill, J., Analysis of the Phenomena of the Human Mind, ch. 3. 
Locke, J., Essay concerning Human Understanding, Bk. H, ch. 33. 
Manaceine, M. de. Sleep (trans.), ch. 4. 

Judd, C. H., Psychology, General Introduction (2d ed.), ch. 14. 
Void, J. Moiu-ley, Ueber den Traum. 
Hacker, F., Systematische Traumbeobachtungen, Areh.f. d. ges. Psychol., 

1911, 21. 

Bernheim, H., De la suggestion. Part I. 
Pillsbury, W. B., Psychology of Reasoning. 

Practical Exercises: 

Analyze the succession of experiences in one of your dreams. 

Examine the flow of experiences during the past ten minutes, and study 
the interaction between perceptions and thoughts in the series. 

Sit with pencil and paper and note the first word seen in a book opened at 
random. Write down the first idea which it suggests, then the first idea 
suggested by this latter, and so on for a series of 15 or 20 successive 
associations. Class the associations according to type; examine for laws 
of recency, etc. 



CHAPTER XVII 

ATTITUDES 

Permanent Mental Conditions. — As we have repeatedly 
noticed, the mental state at any given moment is determined 
not merely by present stimuli and present nerve impulses, but 
also by the ' set ' or traces which previous stimuli and im- 
pulses have left in the nerve substance. The traces of an 
individual's past mental life serve to modify specific sensory 
experiences and arouse ideational experiences. In addition to 
this they tend to produce general modifications in his mental 
organization which alter the tone of his mental life as a whole. 

When a certain type of experience is constantly repeated, a 
change of set is brought about which affects many central 
neurons and tends to spread over other parts of the central 
nervous system. These changes in the general set of the cen- 
tral system temper the process of reception ; they lead to the 
formation of certain general modes of receiving and integrat- 
ing stimuli. In terms of the subjective mental life these gen- 
eral sets are called attitudes. A man's attitude toward any 
situation which confronts him is quite as important a factor in 
his mental life as the nature of the specific stimuli which enter 
into that situation. 

The specific attitudes which develop during the course of 
life affect one another and result in the formation of general 
attitudes. These general attitudes constitute the various 
phases of the individual's character.^ | 

In the same way the several phases of character become 
organized into the ' general character ' which permeates an 

^ The term character is sometimes used more broadly as a synonym for 
personality; it is also frequently restricted to a single tj^e — moral character. 
There is justification, however, even in popular usage, for the intermediate 
definition adopted here. 



PERMANENT MENTAL CONDITIONS 361 

individual's whole mental life. This summation of one's past 
is called personality. 

Attitudes alter from time to time with the growth of experi- 
ence; but changes of attitude proceed far more slowly than 
the changes of specific mental states. Similarly, character 
alters and develops as our attitudes change or as new attitudes 
arise, but at a much slower rate than the growth of attitudes. 
Personality, which depends upon the interworking of the 
several phases of our character, undergoes a still more gradual 
development and transformation; the growth of personality 
covers the entire period of our life-time. 

1. Attitudes 

Nature and Classes of Attitudes. — An attitude is due to 
repetition of neural processes of one and the same type. Each 
specific experience includes a focus of vivid consciousness and 
a margin or fringe of indistinct elements. The focal com- 
ponent is due to intense impulses which affect the given cen- 
ter. The marginal components are due to faint accompany- 
ing impulses. Since the mode of these faint components, in- 
sofar as it is not due to present sensory stimuli, is determined 
by the set of the neurons, our marginal consciousness reflects 
in great measure the permanent effects of past experiences. 
Our experiences take on a characteristic tinge due to this gen- 
eral set. In any given experience this permanent tinge con- 
stitutes our attitude toward specific stimuli or toward the en- 
tire situation which confronts us. The relation between the 
stimulus and attitude factors is illustrated by comparing the 
experiences of watching a bonfire and a destructive conflagra- 
tion. The sensory stimuli may be substantially alike in the 
two cases, but our response is quite different. We assume 
entirely different emotional and motor attitudes. 

Attitudes are classed according to the type of mental state 
which characterizes them. There are attitudes corresponding 
to each type of experience, but some types are more fully de- 



362 



ATTITUDES 



veloped than others and play a more important part in mental 
life. The principal classes of human attitudes and their 
sensory origin are shown in Table XIX. 

Table XIX. — • Human Attitudes 



Attitude 
Primary : 

Interest 

Desire 

Attention 
Secondary: 

Dispositions 

'Appreciation' 

Social and Moral (Conscience) 

'Proclivities' 

Of Communication 

Of Rational Action 



Mental Basis 

Perception, Ideation 

Peeling 

Conation 

Emotion, Sentiment 

Thought 

Social Situations 

Volition 

Language 

Ideals I 



a. Interest. — Interest is our mode of receiving percep- 
tions of the external world and our attitude toward imagery i 
or thought derived from external stimuli. The experiences] 
which arouse interest are concerned principally with the rela- 
tions of objects and events to one another and to ourselves. | 
The child manifests interest in isolated experiences, that is, j 
in the specific objects and events which are received through j 
the external receptors. The adult is less interested in spe- 
cific occurrences than in their changes, their differences, and] 
similarities. 

In the course of an individual's life-time he builds up a sys- 
tem of meanings and a scale of values. The development of | 
certain meanings fosters his interest in the corresponding 
kinds of objects and events, and the scale of values regulates] 
the degree of interest attaching to each. Interest serves to] 
maintain an experience in the focus of consciousness. Lack] 
of interest results in shifting the focus from one perceptual ot\ 
ideational experience to another. 

Professional baseball players have developed a high degree] 
of interest in the situations involved in the game; the in vet- 



INTEREST 368 

erate ' fan ' acquires a similar interest through constant at- 
tendance. In either case the interest attitude is not itself a 
focal experience. The player and the fan are seldom aware of 
their interest, but they are vividly aware of each situation in 
the game and of each individual play. The interest attitude 
maintains the details of the game in the focus of conscious- 
ness; it inhibits the players from hearing the shouts of the 
spectators, and prevents the spectator from thinking about 
his business problems or leaving the field before the game is 
finished. 

In visual perception interest is associated with the center 
of vision, while the data furnished by the periphery of the eye 
are generally but little noticed. By training one may acquire 
a capacity for observing out of the " corner of the eye " with- 
out moving the eyeball so as to center the objects observed. 
This is brought about by the attitude of interest toward 
peripheral parts of the retina. 

Interest attaches not only to perceptions, but to images and 
thoughts which represent external situations and events. 
Interest in science attaches largely to thought experiences. 
The inventor's interest is aroused when he considers what de- 
vice would produce the desired external resiilt — even before 
he attempts to try it out. So far as we observe, there is no 
essential difference between these ideational attitudes and the 
perceptual attitudes. They are attitudes of the same type 
and are covered by the single term, interest. Moreover, 
interest attitudes differ in degree rather than in kind. The 
quality of interest is the same whatever the specific experience 
to which it attaches. 

b. Desire. — Desire is the attitude which develops in con- 
nection with the systemic experiences, or feelings. It has 
two forms, corresponding to the affective modes of pleasant- 
ness and unpleasantness. Our attitude toward pleasant 
states is called satisfaction. In the case of unpleasant states 
the attitude is something more than the opposite of this — 



364 ATTITUDES 

dissatisfaction; it carries with it a picture of the removal of 
the unpleasantness or of its transformation into pleasantness. 
This attitude is called want, or need. 

The satisfaction attitude is a less distinctive experience 
than want. The pleasantness of the experience itself is the 
dominant factor, and the attitude usually plays an unimpor- 
tant part. But in states of unpleasantness the attitude of 
want tends to share the focus with the feeling of unpleasant- 
ness. While specific systemic ideas are rare, the want attitude, 
which has an ideational tinge, is a most important factor in 
mental life. Through instinctive and intelligent reactions 
the want attitude leads to motor expressions which tend to 
transform the unpleasant state into pleasantness. Our re- 
sponses do not always yield stimuli which fulfill our needs. 
But the want attitude is generally followed by motor impulses 
of some sort, and as adjustment develops, the tendency to 
fulfillment is increased. The satisfaction attitude is more 
often quiescent. 

c. Attention. — Attention denotes our kinesthetic atti- 
tude.^ It is due to marginal kinesthetic elements which pro- 
duce certain minor discharges in the outgoing motor nerves. 
These slight motor impulses are not sufficient to produce gross 
muscular contractions, but they adjust the muscular tension 
and serve to maintain or alter the focus of consciousness. 
When we fix the eye, clench the teeth, wrinkle the brow, etc., 
these motor adjustments assist in maintaining some present 
mental state as focal, or serve to focalize a marginal state. 

In strenuous efforts of attention many different motor ad- 
justments are involved and the impulses are frequently very 
intense. • In thinking out a difficult problem we often draw 
long and deep breaths and maintain the muscles throughout 
the body in a state of rigid tension. These slight secondary 
motor discharges take the place of gross discharges through 

^ The term attention is used, it will be remembered, in a technical sense; 
see p. 141. 



ATTENTION 365 

the ordinary motor channels, which would produce new and 
distracting stimuli, so that we are enabled to pursue unhin- 
dered a train of thought, the main nerve impulse passing from 
center to center in the brain for a long time. 

Attention is not the focusing process itself. Focalization 
occurs as a result of attention. There are also cases of focus- 
ing which occur quite independent of attention and even in 
spite of the attention attitude. A loud sound may produce a 
focal auditory perception despite our every effort to attend to 
a traiti of thought or reasoning. This type of focalization is 
often called involuntary attention. 

Relation of Attention to Interest and Desire. — In popular 
language attention and interest are used almost interchange- 
ably. As a matter of fact attention is the motor attitude, 
while interest is based upon perception or ideational states 
which result from perceptual experiences. They are separate 
factors, though generally found together in one experience. 
Indeed in many experiences interest, attention, and desire are 
so united that it is difficult to distinguish them. We desire 
and attend to that which interests us; we become interested 
in and desirous of what we attend to; or we assume attention 
and interest toward that which we desire. 

The three primary attitudes cooperate in complex experi- 
ences. They are often called motives of life,^ since they serve 
to control and guide the succession of experiences. When 
they appear together they give a specific tone to our mental 
life which is termed striving when the motor component is 
active, and self-control or repression when it takes the form of 
inhibition. 

d. Dispositions. — A disposition is an emotional attitude, 
or one in which emotion or sentiment is a leading factor. 
Emotional attitudes are the most fundamental of all the sec- 
ondary types. They arise through the frequent repetition of 

* Ideals are motives in the same sense, but they are more definite mental 
states. See ch. xv. 



366 ATTITUDES 

similar emotions, which leave a permanent trace in the nerv- 
ous system. 

In civilized man there is almost universally a social tend- 
ency to suppress emotional expression, and this partial sup- 
pression reduces the emotional state to a disposition. The 
emotion of joy simmers down into an inground cheerful dis- 
position; the emotion of anger leads to a hostile disposition; 
the emotion of suspicion to a distrustful disposition. In fact, 
nearly every class of emotion gives rise to a corresponding 
attitude or disposition, as is seen by comparing Table XX 
with the list of emotions in Table XVI (p. 299).^ In some 
cases the social suppression of emotion leads to an attitude of 
a somewhat contrary sort, as in the case of courage, which 
seems to have developed from the emotion of fear. 

Only the leading types are included in the Table. There 
are a great many variations of these types — some of them so 
common as to carry familiar names. We distinguish between 
the overbearing, the superior, the condescending, and the 
pompous attitudes — all variations of the arrogant type. If 
one is accustomed to study human nature he will find no 
difl&culty in applying each of these designations to some of his 
acquaintances. 

The variety of forms assumed by emotional attitudes is in 
striking contrast with the uniformity of the interest phenom- 
enon. The other secondary attitudes show considerable vari- 
ety, though far less than the dispositions. 

1 Table XX is based upon an examination of terms in common use (lan- 
guage psychology), checked up by self-observation. Two difficulties appear 
in testing the list: (1) Popular psychology does not distinguish clearly between 
emotions and dispositions; the same words are often applied indiscriminately 
to both — e.g., cordiality, friendliness. (2) The same term is applied by differ- 
ent writers or speakers to somewhat different dispositions: sullen means one 
attitude to one observer, another to another. Any such table can only be 
treated as tentative at the present stage of investigation; a satisfactory list 
of emotions and dispositions seems to require quantitative determination of 
the various glandular and metabolic activities which accompany them; we 
are not yet in a position to make these determinations. 



DISPOSITIONS 



367 



Table XX. — Human Dispositions 



1. ExTi^r 


:saive 


2. Reproductive 


Attitude 


Emotion 


Attitude 


Emotion 


Cheerful 


Joy 


Affectionate 


Love 


Despondent 


Grief 


Lascivious 


Lust 


Dazed 


Shock 


Jealous 


Jealousy 


Frivolous 


Mirth 


Motherly 


Tenderness 


Zealous 


Ecstasy 






Erratic 


Restiveness 






Romantic 


Exuberance 






Devout 


Wonder 






3. Defensive 


4. Aggressive 


Attitude 


Emotion 


Attitude 


Emotion 


Cowardly 


Fear 


Hostile 


Anger 


Courageous 


" 


Vindictive 


Hatred 


Aversion 


Disgust 


Malicious 


Envy 


Cautious 


Timidity 


Ambitious 


Pride 


Reserved 


Shame 


Arrogant 


" 


Servile 


Awe 


Bold 


Exultation 


5. Social 


6. Instinctive and Sentimental 


Attitude 


Emotion 


Attitude 


Basis 


Devoted 


Affection 


Miserly 


Acquiring instinct 


Friendly 


Cordiality 


(Avaricious)' 




Compassionate 


Pity 


Orderly 


Cleanliness 


Attachment [ 


( Gratitude 
( Admiration 


Nomadic 


Wandering instinct 


Loyal ) 






Antagonistic 


Detestation 


Credulous 


Belief 


Sullen 


Revenge 


Skeptical 


Disbelief 


Distrustful 


Suspicion 


Perplexed 


Doubt 


Supercilious 


Scorn 


Biased 


Belief and Disbelief 



Popular psychology distinguishes between a disposition, 
which is a more or less permanent attitude, and a mood, which 
is liable to frequent fluctuation. The distinction seems valid, 
but it is of social rather than psychological importance. Our 
emotional attitudes become established by slow degrees, and 
the border line between a passing mood and an inground dis- 
position is indefinite. 

Sentimental attitudes are closely related to emotional atti- 
tudes; this probably accounts for the popular confusion be- 



S68 ATTITUDES 

tween the mental states which generate them. Doubt gives 
rise to a perplexed attitude, while a mingling of strong belief 
with strong disbelief produces a biased or prejudiced disposi- 
tion. Certain attitudes are apparently derived from instincts 
directly, with no emotional intermediary; as for instance the 
avaricious and orderly dispositions. 

The wide reach of emotional attitudes is observed in the 
opinions and judgments expressed in every-day life. They 
color even biographical estimates and histories — particu- 
larly those written nearly contemporaneously with the times 
they portray.^ 

Most of our dispositions, like our emotions, are imperfectly 
adjusted to the conditions of civilized life. If we test our 
emotional attitudes (or better those of others) by social ex- 
perience, we observe that the emotional component generally 
hampers the intercourse of man with man. The servile dis- 
position is as disconcerting as the arrogant. The exceptions 
(loyal, compassionate, etc.) are precisely those dispositions 
which promote mutual cooperation and which therefore run 
parallel with the social attitude of our ideal life. 

^ The following fictitioijLs illustration contains contrasted statements by 
two opposing parties. They embody the same facts. The sole difference is 
in the attitude, marked by changes in the emotional words: 

The Judean government has permitted the criminal machinations of va- 
rious societies and associations directed against the Roman dominion and 
has tolerated unrestrained language on the part of its citizens, glorification 
of the perpetrators of outrages, and participation of Judean officers and func- 
tionaries in subversive agitation against Roman authority. It has permitted 
an unwholesome propaganda in public instruction. In short it has per- 
mitted all manifestations of a nature to incite the Judean population to hatred 
of the Roman state and contempt of its institutions. 

The Judean government has fostered the patriotic activities of various 
societies and associations directed against the Roman usurpation and has 
sanctioned outspoken expression on the part of its citizens, glorification of 
the heroic resisters of oppression, and participation of Judean officers and 
functionaries in agitation for the overthrow of Roman tyranny. It has 
fostered a healthy propaganda in public instruction. In short it has fos- 
tered all manifestations of a nature to awaken the Judean population to 
hatred of the Roman state and reprobation of its institutions. 



DISPOSITIONS 369 

Since our dispositions are of systemic origin they are more 
subject to central control than phenomena of external origin. 
But they are less under control than kinesthetic phenom- 
ena. From the pedagogic standpoint the early training of 
emotions and dispositions seems even more important than 
the perfection of motor habits. 

e. Other Secondary Attitudes. — The most important devel- 
opments of attitude in connection with the higher secondary 
states are found in the sphere of thought and conduct. 

Attitudes of thought (appreciation ^) develop in a variety 
of different directions. Certain thought attitudes arise from 
sentiments when the feeling component is reduced to a mini- 
mum. One of the most important attitudes in the higher 
mental life of man is the interrogative or problem attitude, 
which is closely related to doubt, with the ideational factor 
emphasized. This attitude is not only experienced when we 
put specific questions to others or set ourselves to solve a 
problem, but it furnishes the basis for scientific investigation 
and rational thinking generally. 

The leading types of thought attitudes are shown in Table 
XXI (1). The interpretive and evaluative attitudes per- 
meate our perceptual life as well as our thoughts. We be- 
come trained to observe differences in kind and quantitative 
differences among the objects which we perceive. An inter- 
pretive attitude toward thought is cultivated by modern edu- 
cation. Writers learn to appreciate subtle distinctions in the 
meaning of words. Even the average reader acquires an atti- 
tude toward individual words. James speaks of the feeling 
which attaches to such minor words as and, if, but, and by.^ 
These are really instances of the appreciative attitude, which 
leads us to interpret or evaluate the relations of words in a 

1 Strictly speaking the term appreciation applies only to the interpretive 
attitude and those that follow in the table. 

2 Psychology, p. 162. James applies the term feeling to any indefinite 
mental state or attitude. 



370 



ATTITUDES 



Doubt (feeling marginal) 
Belief ( " " ) 

Memory coefficient focal 
Purpose (volition marginal) 
Associative thought 



Meaning 

Value 

Esthetic sentiment (feeling marginal)j 

Rational thought 



sentence as well as relations of objects. Rational thought 
develops certain attitudes of consecutive thinking, such as the 
analytic, constructive, and critical. 

Table XXI. — Higher Human Attitudes 
1. Attitudes of Thought ('Appreciation') 
Attitude 
Interrogative (Problem attitude) 
Impartial 
Retrospective 
Anticipatory 
Desultory 
Naive 

Interpretive 

Evaluative 

Esthetic appreciation 

Rational, Logical 

Analytic 

Synthetic, Constructive 

Critical 

2. Social and Moral Attitudes 
(Conscience) 
Conciliatory, Cooperative 
Contrary, Competitive 
Accusatory, Condemning 
Laudatory, Approving 
Judicial 

Self-centered, Self-satisfied 

Altruistic 

Penitent 

Suppliant 

Forgiving 

Prudish 

Irresponsible 

Superstitious (fetish and tabu) 

Duty-bound (of moral obligation) 



3. Other Secondary Attitudes 

(a) Motor Attitudes ('Proclivities'): 
Persevering, Obstinate 
Vacillating 

(b) Language Attitudes: 
Receptive 
Expressive 
Voluble 
Reticent 

(c) Ideal Attitudes: 
Idealistic 
Practical 
Sensual 
Scientific 
Artistic 



In our relations to other men and to society at large a num^ 
ber of important social attitudes have arisen (Table XXI, 2).] 



OTHER SECONDARY ATTITUDES 371 

A satisfactory classification of these is difficult, because they 
shade from emotional or volitional experiences into the 
sphere of conduct by gradual degrees. Thus the fault-finding 
{reproachful) attitude contains a large element of emotion 
but is tinged with a ' sense ' of obligation toward society; the 
inculpatory attitude of a public prosecutor, on the other hand, 
is ethical with scarcely any emotional tinge. Midway be- 
tween these is the accusatory attitude so frequently noticed in 
modern political and community life. 

The term conscience is commonly applied to attitudes of 
conduct (moral attitudes). In general usage it has a decided 
emotional tinge; and this use is historically justified, since the 
emotions have been a potent factor in developing our social 
ideals and conduct. But the notion may be extended to such 
unemotional phenomena as the judicial attitude and the 
" sense of moral obligation " (the duty-bound attitude). 

It should be recognized by psychologists that while the 
social and moral attitudes as experiences evolve in much the 
same way in all races, the situations which evoke them vary 
greatly in different communities and stages of civilization. 
Or to put it the other way around, the same act or the same 
objective situation may yield very different attitudes in 
various races and culture-stages. 

Among the ancient Romans it was the accepted custom to 
expose to death new-born children if they were deformed or 
weak. The same custom holds today among the Eskimos. 
In other societies, such as our own, these weaklings are es- 
pecially cared for and protected. In many communities the 
child is regarded as the slave of his parents, who do not recog- 
nize any obhgation toward their offspring except to feed and 
clothe them. In other communities there is a recognized ob- 
ligation on the part of the parents to educate their children 
and fit them for their life-work. Whether the attitude of 
obligation is assumed in a given situation depends upon the 
traditional customs of the people. 



372 ATTITUDES 

The sexual and marital code is subject to similar variation. 
Among uncivilized tribes some insist upon marriage within 
the clan; others insist quite as strongly upon exogamy. In 
certain communities polygamy prevails, while in most modern 
civilized communities the traditional social rule is monogamy. 
From the standpoint of systematic ethics these differences are 
of fundamental importance. The science of ethics seeks to 
determine which code is higher and better. But psychology 
is interested in duty chiefly as a datum of experience. We are 
concerned with the attitude — not with the social and moral 
worth of the act or situation in the evolutionary scale. 

An attitude is generally a marginal component of the pres- 
ent mental state. This is as true of moral attitudes as of 
other types. When we act in a friendly way, speak the truth, 
or refrain from hurting another's feelings, we are usually not 
distinctly aware that a moral attitude is involved. But on 
occasion the moral experience becomes focal, more especially 
when our conduct is at variance with a recognized moral code. 
The mental state thus aroused is a moral ideal rather than an 
attitude. In such cases it is the feeling components that are 
apt to be especially focalized. In the popular conception of 
conscience this predominance of the affective side is empha- 
sized. The well-known ' Puritan conscience ' of the Anglo- 
Saxon race belongs to this type. 

A clearer conception of the duty attitude and other moral 
ajid social attitudes is attained if we realize (1) that in normal 
circumstances they operate as readily when they are only 
marginal as when they are focalized; (2) that under civilized 
conditions the affective component — the ' feeling ' part of 
the attitude — is more often a hindrance than a help to the 
adjustment of social relations. 

The remaining classes of mental states furnish less prom- 
inent attitudes. The use of language results in receptive 
and expressive attitudes and in the voluble and reticent types. 
Volition develops the persevering attitude, with its variant, 



OTHER SECONDARY ATTITUDES 373 

the obstinate; in the other direction it leads to the vacillating 
attitude. We may call these motor attitudes 'proclivities. 
Ideals give rise to the idealistic attitude, the 'practical, sen- 
sual, and other types. (Table XXI, 3.) 

Collateral Reading: 
Titchener, E. B., Psychology of Feeling and Attention, chs. 5, 8. 
James, W., Psychology, ch. 13. 
Judd, C. H., Psychology (2d ed.), chs. 7, 15. 
Angell, J. R., Psychology, chs. 4, 21. 

Titchener, E. B., Text-Book of Psychology, sees. 75-84, 138-141. 
Pillsbury, W. B., Fundamentals of Psychology, ch. 7. 
Breese, B. B., Psychology, ch. 3. 
Calkins, M. W., First Book in Psychology, ch. 6. 
Pillsbm-y, W. B., Attention. 
Ribot, Th., Psychology of Attention (trans.). 
Arnold, F., Attention and Interest. 

Practical Exercises: 

Compare the stimulus effect and your attitude in reading a novel, in watch' 

ing a ball game, in discussing some question with a friend. 
Analyze the attitude of pique ('being peeved') in yourself and others, 

including its characteristic manifestations; also the jealous and devout 

attitudes. 
Examine some important congressional or legislative debate; determine to 

what extent the attitude of participants was conciliatory, accusatory, 

and judicial. 



CHAPTER XVIII 
CHARACTER AND PERSONALITY 

2. Character 

Nature of Character. — Character is the general rating of 
an individual in any specific phase of mental life. It denotes 
the degree and trend of his mental development in that par- 
ticular sphere. In popular language the term is usually lim- 
ited to a man's moral standing or rating. In psychology it 
has a broader application; it includes also his rating in the 
perceptual and ideational life, in the hedonic life, and in the 
motor life. The same man may be rated as malevolent, keen, 
sanguine, and energetic. These represent different phases of 
his character. Each phase of character may embrace a num- 
ber of independent traits. 

As the child grows toward maturity the same types of 
experience are constantly repeated with minor variations. 
With each repetition his attitude becomes more clear-cut and 
definite. Many such attitudes develop and modify one an- 
other. The interworking of various attitudes in each sphere 
of experience results in building up our general attitude, or 
character. Our character forms the background of our sub- 
jective mental life, and the character of other individuals may 
be observed objectively through their behavior. 

One's specific attitude in any complex situation is deter- 
mined by the general attitudes which have been built up in 
his past. A man's character — that is, his general attitude 
toward the environment at large, toward others, toward him- 
self, and toward ' life ' — is indicated by the trend of his con- 
crete actions. Given a sujQBcient number of specific responses, 
it is possible for an observer to " size a man up " pretty 
accurately. 



NATURE OF CHARACTER 375 

Strictly speaking, a man's character is not the rating which 
his fellows actually give him;^ for such ratings are liable to 
error. Character is the rating which the individual would 
receive if one could appraise him correctly. 

The principal lines of character development correspond to 
the fundamental types of sensation (internal, external, kines- 
thetic), with a fourth which arises from social relations. 
These phases of character are called 

Temperament 
Intellectuality 
Skill 
Morality 

a. Temperament. — Temperament is the phase of char- 
acter based upon an individual's hedonic attitudes; it ex- 
presses the development of his systemic life. We rate a 
man's hedonic standing quite apart from his intellectual or 
moral standing. 

The older psychology recognized four kinds of tempera- 
ment, the choleric, melancholic, sanguine, and phlegmatic. 
This classification was based upon a doctrine of internal se- 
cretions which though in the main erroneous contained a 
germ of truth. 

Temperament is possibly correlated with the modes of 
heart action. The heart-beat may be strong or weak, and 
it may be rapid or slow. Combining these pairs we get four 
varieties of temperament which correspond to the classic 
types. The sanguine temperament represents strong and 
slow activity, the melancholic weak and rapid, the choleric 
strong and rapid, and the phlegmatic weak and slow.^ 

An objection to the four-fold division is that it does 
not take account of the positive and negative phases which 
form the differential basis of hedonic phenomena. The 

^ This tentative rating is a man's reputation. 

2 In the classical scheme sanguine = rapid-weak, melancholic = slow- 
strong. 



Pleasant 


Jovial 


Unpleasant 


Melancholic or Saturnine 


IndiflFerent 


Phlegmatic 



376 CHARACTER 

optimist and the pessimist would both belong to the sanguine 
type. 

A more exact classification of temperaments is based upon 
both the mode of activity and the quality of hedonic tone. 
The former has two phases, active and passive; the latter 
three phases, pleasant, unpleasant, and indifferent. Com- 
bining these two groups of characteristics we obtain the six 
varieties of temperament shown in Table XXII. 

Table XXII. — Classification of Temperaments 
Mode of Activity Hedonic Tone Temperament 

{Pleasant Sanguine 

Unpleasant Choleric 

Indiflferent Mercurial 

Passive -j 

b. Intellectuality. — Intellectuality or intellect ^ is an indi- 
vidual's general rating on the ideational side. Broadly speak- 
ing, this includes the development of attitudes derived from 
perceptions and imagery as well as those derived from the 
secondary processes of thought, judgment, and reasoning. 

Perception and imagination are generally less important 
factors in the individual's intellectual character than memory, 
judgment, and reasoning, though at times they enter as 
prominent factors. The man whose perceptions are clear has 
usually a better developed memory than his fellows; a highly 
developed imagination serves the inventor and artist better 
than a corresponding growth of judgment and reasoning. 

The growth of intellect depends more upon ' social at- 
mosphere ' and training than on the variety and nature of 
general external stimuli. A person like Helen Keller, de- 

' Often called intelligence; this term is used technically in a slightly differ- 
ent sense (ch. vii). It includes all forms of acquired adeptive responses, 
whether intellectual, skillful, or moral. 



INTELLECTUALITY 377 

prived of the two most important sources of information, 
sight and hearing, may through careful education attain as 
high an intellectual level as one provided with all the usual 
avenues of information. But intellect depends upon inherited 
nerve structure even more than on training or other environ- 
mental influences. This is demonstrated when we compare 
the intellectual rating of the dog or the worm with that of low- 
grade human individuals. 

Intellectual development proceeds in two distinct direc- 
tions, which correspond in a figurative way to the spatial di- 
mensions of breadth and height. Breadth denotes the number 
of different traits which the individual has developed; height 
means the amount of growth in each independent attainment. 
The breadth of our intellect depends essentially upon the 
complexity of our inherited nerve structure, while its height 
depends more largely upon education. 

Both breadth and height must be taken into account in 
rating an individual. For example, there are instances of 
mathematical prodigies and memory geniuses who fail to 
reach the average intellectual level in other respects. On the 
other hand there are men possessed of small snatches of 
knowledge and mental capacity in many directions who fail 
to measure up to the average in any one particular. A man 
of high-grade intellect is one whose attainments are both 
broad and highly developed. 

Various attempts have been made to measure intellectual 
attainment. So far they have met with only partial success. 
The diflSculty has been to distinguish the independent phases 
of intellect and to estimate their relative importance. A 
most important step in this direction is the scale devised by 
Binet and Simon for measuring the mental growth of children. 
This scale consists of a large number of tests involving various 
sorts of mental states (perception, memory, imagery, and 
reasoning), and so graded that the child's success in perform- 
ing the tests successfully, measured and averaged, will indi- 



378 CHARACTER 

cate his general intellectual level. For example, the growth 
of memory is tested by ability to repeat sentences of various 
lengths and series of numbers of three, four, five, and more 
figures. Rational thought is tested by making statements 
containing some absurdity, which the child is asked to point 
out. 

The success of the Binet Scale as a measure of intellect is 
due to the fact that the intellectual development of children 
is relatively simple; they have not yet developed a great va- 
riety of complex mental traits. By examining all the chil- 
dren in a large school and comparing those of each age, it is 
found that 50% of the 10-year-old children succeed in a cer- 
tain number of these tests. This is taken as the measure of 
the average level of intellect at that age. The same procedure 
is used in determining the standard for 9 years, etc. Those 
children of 10 years who only attain the 9-year standard are 
said to be 1 year backward; their 'mental age' is 9 years. 
And so for other ages. 

In attempting to apply mental tests to adults a difficulty 
arises from the great differences in breadth of development. 
A man may be highly developed along certain lines and defi- 
cient in others. It has not yet been determined satisfactorily 
how to compare these different attainments with one another 
so as to represent fairly the individual's mental level. Re- 
cently a set of mental tests for adults has been devised for 
use in the United States Army which promises good general 
results; but this is only a beginning. 

A mental scale for adults, to be complete, should include 
separate tests for each kind of intellectual state which devel- 
ops independently of others. It should distinguish also be- 
tween those traits which have been developed by special 
training or schooling, and those which grow up under the 
ordinary influences of social environment. The latter seem 
to deserve a higher rating than the former. Mere scholarship 
and information do not signify so high a degree of intellectual 



INTELLECTUALITY 379 

attainment as the less cultivable processes which underlie 
them. 

In applying mental tests special care should be taken that 
the results are truly representative. If the mdividual tested 
has been ' coached,' his answer to a question supposed to in- 
volve reasoning may be really a feat of memory. A phono- 
graph, supplied with the proper record, might yield results 
indicating a superlative degree of intellectuality according to 
the scale. Such a result indicates merely the intellect of the 
individual who prepared the record. Unless due care is taken 
in giving a mental test (or a college examination for that mat- 
ter), the results may indicate the intellect of the ' coach' — 
not the mental level of the testee. 

In the mental life of man intellect is a far more important 
phase of character than temperament. In our relations with 
the social environment it is useful to cultivate special tem- 
peramental traits and inhibit others; but the development of 
intellectuality contributes more to success and happiness in 
life than the cultivation of temperamental character. 

c. Skill. — Skill is the motor character of the individual. 
It means the rating of his development on the kinesthetic side. 
Like intellectuality, the growth of skill depends upon environ- 
ment and inheritance. The environmental influences include 
general physical environment, social suggestion, and special 
training. The inherited factors include the individual's com- 
plex nervous system and effector organs. 

Nerve structure is far more important than elaborate 
motile organs in developing skill. The presence of muscles is 
essential to movement; but the coordination and fine adjust- 
ment of movements is controlled by the central nervous sys- 
tem. A study of handwriting will demonstrate this. First 
write your name in the ordinary way; then write it in very 
small letters, using only finger-movements; then keep your 
fingers rigid and use only the wrist; finally write your name in 
large letters on the blackboard, using only arm movements. 



380 CHARACTER 

Although the muscles involved are dijfferent in each case, 
there is found to be a general similarity between the several 
results; ^ the individuality of a man's handwriting is due to 
characteristics of the impulses from the brain centers, not to 
the constitution of the muscles. 

Skill, like intellectuality, develops in two dimensions, 
breadth and height. Breadth is measured by the number of 
independent motor acts which the individual can perform. 
Height is the degree of perfection in performance. 

The great breadth which characterizes the motor develop- 
ment of civilized man will be realized if we attempt to list the 
acts of every-day life. The catalogue would include such 
varied acts as eating, dressing, writing, drawing, orating,, 
needle-threading and sewing, building a house, juggling balls, 
and a host of other performances. In comparing the motor 
character of individuals, and more especially in rating 
the comparative development of various races, breadth of 
skill is an important factor to consider. 

On the other hand, height — the individual's degree of suc- 
cess in performing any specific type of activity — furnishes a 
more adequate index of skill. In determining height of motor 
attainment two separate factors must usually be measured: 
temporal s'peed and spatial accuracy. In tests of skill we seek 
to determine (1) the number of errors or amount of inaccu- 
racy, and (2) the time which it takes to perform the given 
act. 

It is often difficult to estimate the relative value that 
should be attached to these factors. In certain kinds of work 
accuracy (precision) is of far greater importance than speed; 
in other cases the opposite is true. A telescope lens, for ex- 
ample, must be ground to the utmost degree of accuracy, re- 
gardless of time expended. A ready-made shirt or shirt- 
waist on the other hand must be finished quickly in order to 

^ A similarity is also reported between the left-hand writing of those who 
have lost their right arm, and their former right-hand script. 



SKILL 381 

reduce the cost of production; irregularities in the cutting are 
taken as a matter of course. 

How far such economic valuations should be carried over 
into psychological testing is problematic; but some criterion 
of the relative importance of the two factors is essential. Oc- 
casionally conditions may be so arranged that speed and 
accuracy are reduced to a single variable. In a certain tap- 
ping test the individual is required to insert a plug into a 
series of holes in succession, as rapidly as possible; each inser- 
tion produces an electric contact. If the testee fails to strike 
the proper hole at first he must correct the error before pro- 
ceeding to the next hole. Here the space error is transformed 
into a time error; the inaccuracy factor is eliminated en- 
tirely and speed is the only variable. 

A scale of skillfulness, like the scale of intellectuality, 
should include a great variety of typical, independent acts, 
if it is to indicate breadth as well as height of attainment. 
Up to the present, the construction of a measuring scale 
for skill has not progressed so far as the scale for intellect. 
The importance of intellect seems to have been somewhat 
over-emphasized in modern civilization. We are beginning 
to recognize today that skill is an essential phase of human 
character. 

d. Morality. — This is the phase of character concerned 
with the individual's relations to his fellows. Morality de- 
pends upon our social existence. A man living like Robinson 
Crusoe in solitude, with no other human beings about him, 
has practically no moral duties. Even such an imaginary 
case, however, needs qualification: a castaway lives in the 
hope of rescue and acts with reference to his possible rescuers ; 
he expects at least that someone will discover his remains 
and he orders his life accordingly. For most men social ex- 
periences play a dominating role in mental life. In civilized 
communities moral character is quite as important a phase of 
character as any of those which depend more directly upon 



382 CHARACTER 

sensory data. The popular tendency, in fact, is to magnify it 
at the expense of all other phases.^ 

The development of moral character proceeds in the di- 
rection of height rather than breadth. Our range of social 
relationships expands slowly. Family relations include a 
few different types : filial, parental, and marital. Commmiity 
life includes the general relationship of man to man and a 
number of specific relationships: friendship, business deal- 
ings, community interests, etc. Beyond this lie a group of 
broader social relations — to our country, our race, and 
mankind. 

Far more significant than the range of social relations is the 
degree to which an individual enters into these relations. 
Height of moral character is measured by the individual's 
success in acting so as to benefit his fellows and avoid doing 
them injury. 

Morality is rated largely in terms of motor expression, or 
conduct. A man's moral character is measured not so much 
by his feelings and thoughts as by what he does or neglects to 
do. Yet in a scientific rating of moral development all three 
sensory sides of mental life are to be considered. Sympa- 
thetic or antipathetic emotions, social or anti-social thoughts, 
are potent factors in determining our actions toward our fel- 
low men. A scale of morality, if one could be devised, would 
take into account the individual's social thoughts and feelings 
as well as his actions. 

Moral character is quite as susceptible to directive training 
as intellectuality and skill. While a child gains many of his 

^ The study of moral character is usually assigned to a distinct branch of 
science called ethics, which occupies the border line between psychology and 
sociology. A distinction is often made between social psychology and ethics 
in the narrower sense. Social psychology investigates how men customarily 
act in relation to one another; ethics is limited to determination of the princi- 
ples according to which they ought to act. It would seem more scientific to 
treat these two phases together; for the scientist determines how men ought 
to act only as a result of determining how they do act. 



MORALITY 383 

fundamental principles of morality by suggestion from the 
* unorganized ' social environment, the organized moral edu- 
cation which he receives in the home, the school, and the 
church are of the utmost importance in enabling him to apply 
these principles correctly. 

3. Personality 

The Self. — Personality is the general rating of an indi- 
vidual. It embraces all the various phases of one's character 
— temperament, intellectuality, skill, and morality. Per- 
sonality sums up the total mental constitution of a human 
being at any stage of his development; in other words, it is 
the man's ' general character.' 

We may distinguish between personality and individuality. 
The study of a man's personality is an attempt to measure or 
rate him according to the standards which are common to 
human beings generally. The study of his individuality is 
an attempt to bring out the differential characteristics which 
mark him off from others. If we investigate a man's hand- 
writing as an index to his temperament, intellectuality, and 
skill, we are studying this particular man's personality. On 
the other hand, if our object is merely to note the idiosyn- 
crasies of his script, the study becomes one of individuality. 
The same is true of any similar investigation. 

As a psychological term, personality denotes the man's 
combined rating in the several phases of mental life, while 
individuality is the sum total of his variations from the aver- 
age. Personality and individuality, taken together, consti- 
tute the self. 

Psychology as a science is not especially interested in indi- 
vidual differences,^ except so far as they may be traced to the 
influence of heredity, organic defects, specific training, social 
environment and occupation, and other general factors. To 

1 Applied psychology, which is an art rather than a science, is almost 
wholly interested in these differences. 



384 PERSONALITY 

this extent they are investigated in the branch called indi- 
vidual psychology. General psychology is the investigation of 
the common features of mental life, which are summed up 
in personality. 

The self, or mind, or personality, is not to be regarded as 
an abstract being, an entity distinct from the specific phe- 
nomena of mental life.^ Man's self or personality is the sum 
total of his specific experiences insofar as they represent the 
results of organization. Each new experience modifies our 
personality. It is not merely an accretion to the sum of our 
mental data, but it alters our attitude toward the external 
world and makes a permanent impression, small or great, 
upon our general character. This permanent modification of 
the individual through experience is characteristic of all the 
higher organic species, but preeminently of man. 

So far the attempts at a scientific measurement of human 
personality have met with little success. Most of the essays 
and books on personality are written by amateur psycholo- 
gists, who have no appreciation of the real problems involved. 
They emphasize certain striking individual features, or deal 
merely with a few distinctive traits of character. The 
trained psychologist is apt to avoid the problem altogether. 

The reason for this is plain. Measurement of personality 
involves determination of the relative importance of the sev- 
eral distinct phases of character. In a general scale of human 
' mentality ' what proportion should be allowed to intellect.? 
How much should temperament, skill, and morality count? 
Where such disparate factors are concerned the only satis- 
factory criterion, apparently, is the amount which each factor 
contributes toward the adaptation of our active processes to 
the conditions of our environment. It is readily seen that in- 
tellect is a highly important factor in promoting adaptation, 
and that temperamental growth is detrimental to smooth ad- 
justment rmless subjected to careful control by training. Up 
^ See Appendix, "Personification of Natural Phenomena," p. 433. 



THE SELF 385 

to the present psychologists have not advanced very far 
toward a quantitative expression of the relations between the 
several factors.^ 

Personal Identity and Multiple Personality. — In most 
human beings the mental states are organized into one single 
group and one continuous chain of experiences. The greater 
part of one's past experiences admit of being brought into 
relation with the present if the proper neural connections are 
made. My conscious life stretches back as far as I can re- 
member, and every event which I recall is felt to belong to one 
and the same " myself." My present thoughts and feelings 
and activities, too, are tinged with a certain scarcely de- 
scribable element which may be called the " sense of owner- 
ship." Sully ^ attributes this component to the vague (mar- 
ginal) memory background of past experience which enters 
into the present mental state. 

The ' me ' component in memory experiences and the 
' mine ' component in new present experiences, taken to- 
gether, constitute the experience of personal identity. This 
corresponds to a fact of mental life — that ordinarily the 
whole mass of an individual's experiences actually belong to 
one continuous series; that his mental life, though complex, 
is a unity. 

In certain conditions this unity of self is broken. Groups 
of experiences may be dissociated from the general mass and 
become organized into a more or less definite personality of 
their owjn. This occurs most noticeably in functional de- 
rangements of the central nervous system, producing condi- 
tions known as hysteria. But similar phenomena may be 
observed in normal life. 

* Split off ' mental states occur separately as subconscious 

1 It should also be remembered that we have as yet made little headway 
toward explaining the very complex phenomena which enter into personality 
in terms of neural operations. 

» Illusions, p. 252. 



886 PERSONALITY 

experiences (ch. viii), though it is difficult to detect them 
unless they are well' organized into distinct personalities. 
Many of our habitual acts, which to the performer appear 
unconscious, are most probably part of subordinate or sub- 
conscious personalities. 

When one is able to perform two separate acts at once, 
such as cutting his food and planning a lecture, or knitting 
and talking, the two acts probably belong to separate mental 
organizations or personalities. Individuals susceptible to 
trance or hypnosis may be engaged in conversation and at the 
same time may write ' automatically ' on some entirely differ- 
ent topic. In most cases of this sort, and in the dissociated 
states of hysteria, one of the personalities is subordinate to 
the other. The data from the minor self may be brought into 
relation with the major self, as when the lecture-planning self 
takes charge of the feeding operation, or the talking self turns 
attention to the knitting. These are typical cases of subor- 
dinate consciousness, or secondary personality. 

There are occasionally pathological instances where the 
secondary personality becomes so completely organized as 
to constitute a separate self. The patient leads two distinct 
lives. Either there is in one state no memory of the experi- 
ences and doings in the other state; or state A may be remem- 
bered in state B, but not the reverse. The temperament and 
other phases of character may be quite different in one per- 
sonality from the other. In Janet's historic case,^ Leonie 1 
was serious, slow, and timid; Leonie 2 was gay and restless. 
In such instances the secondary self has developed into a 
second primary self. This phenomenon is called co-con- 
sciousness or dual personality. 

There is something fascinating to most of us in the study 
of these unusual phenomena. The casual observer regards 
them as weird and uncanny — perhaps as demon-possession 

^ Rev. philos., 1888, 25, p. 260 (quoted by James). See Pierre Janet, 
Automatisme psychologique, pp. 132-133, 490-491. 



MULTIPLE PERSONALITY 387 

or manifestations of a mysterious spirit-world. To the stu- 
dent of psychology all these instances, whether of second- 
ary personality or of dual personality, serve rather to em- 
phasize the general unity of the self. Multiple personality 
is the exception. For the most part our experiences are all 
woven together and 'organized ' into a single personality: 
myself. 

Self-Consciousness. — Our notion of self (the self-notion) 
is the focalized experience which arises in connection with 
this unity of personality. It develops from certain sensory 
experiences. Even in early life the child perceives his body 
through the external senses, and to this experience is attached 
a mass of organized systemic and kinesthetic sensations. 
Our feelings have a common tinge; our conative states are 
closely related together. The complex experience formed by 
the integration of all the sensory and imagery components 
which refer to the child's own body and its activities consti- 
tute his self-perception or self-feeling. 

When thought and language develop the self-feeling is in- 
tegrated into a thought, to which a name is attached. In the 
earlier stages this is not so much a self-notion as an object- 
notion. The child calls himself ' Baby,' or uses his own 
name: "Jack is himgry "; "Show it to Baby." His own 
personality stands on the same footing as that of other human 
beings. This first step may be called the objective stage of 
the self -experience.^ 

When personal pronouns come to be used the notion of self 
is sharply differentiated from the general notion of ' human 
beings.' This second step is the subjective stage; the child 
comes to recognize the peculiar relation of his own body and 
its activities to his conscious experiences. 

The true self -notion dates from this stage. It develops 
constantly throughout life, especially among civilized and 
reflective beings. We ' read ' a personality with systemic 
^ Baldwin calls it the jwo/edice stage. Soc. andEth.Interp. (4thed.), P- 13. 



388 PERSONALITY 

and kinesthetic experiences like our own into other human 
beings, and even into lower animals and inanimate objects. 
This ejection of our self-experiences into others is some- 
times considered a third stage in the growth of the self- 
notion. 

The notion of self is usually called self -consciousness. The 
term self-consciousness is sometimes limited to the reflective 
or focalized thought of self, when we attend to the specific 
characters of the self-experience. The distinction between 
self -consciousness as an attitude and the focalized self -experi- 
ence is emphasized in philosophical inquiries, but it is of no 
special moment in psychology. It is merely one phase of the 
distinction between naive and scientific observation of phe- 
nomena which was pointed out in an earlier chapter. We 
may distinguish in just the same way between e very-day 
perception of an object and critical examination of this per- 
ceptual experience, as between ordinary and reflective obser- 
vation of self. 

-Personality is the final step in the synthesis of experiences. 
It completes our survey of the central side of mental life. 

Summary of Chapters XVI to XVIII. — In preceding chap- 
ters (xii-xv) we discussed the various types of central states 
which occur in mental life. But mental life is not a mere 
grouping of states at a given moment. It consists in a con- 
stant change and succession of states. 

Two distinct types of succession were noted, with quite 
different principles of change. In one type (the perceptual) 
the chief cause of change is the activity of the environment; 
here the primary source of the succession is the outer world, 
though the stream is modified by various internal factors. 
In the second type (thought-trains) the chief cause of change 
is the ramified connections of the central neurons and the 
retention phenomenon; the primary source of the succession 
in this case lies within the nervous system. 

The general succession of experiences is brought about by 



\ 



SUMMARY OP CHAPTERS XVI TO XVIII 389 

a combination of both sets of factors, external stimuli and 
intra-organic conditions. In other words, the stream of men- 
tal life is molded in part by our present environment, partly 
by our neural constitution; the latter is determined in part 
by heredity and partly by our past experiences (ch. xvi). 

The succession of mental states results in the formation of 
more or less permanent mental conditions. These constitute 
our attitudes, which appear in every phase of mental life 
(ch. xvii). 

Attitudes consolidate along the main lines of mental devel- 
opment, forming the several phases of character — tempera- 
ment, intellect, skill, and morality. A man's character in 
each of these phases denotes the variety and degree of his 
development on that specific side of mental life. 

Personality is the sum total of character. It denotes the 
variety and degree of man's mental development taken as a 
whole. Individuality denotes his specific and peculiar devel- 
opment in any direction, which marks him off from his fel- 
lows. Personality and individuality, taken together, consti- 
tute the self (ch. xviii). 

Collateral Reading : 

James, W., Psychology, ch. 12. 
Angell, J. R., Psychology, chs. 22, 23. 

Titchener, E. B., Text-Book of Psychology, sees. 135-137, 148. 
Judd, C. H., Psychology (2d ed.), ch. 13. 
Breese, B. B., Psychology, ch. 20. 
Pillsbury, W. B., Fundamentals of Psychology, ch. 16. 
Jastrow, J., Temperament and Character. 
Ach, N., Ueber den Willensakt und das Temperament, sec. 21. 
Binet, A., and Simon, Th., Method of Measm-ing the Development of In- 
telligence in Children (trans.). 
Book, W. F., The Psychology of Skill. 
Thorndike, E. L., Individuality. 

Baldwin, J. M., Social and Ethical Interpretations, ch. 1. 
HoUingworth, H. L., Vocational Psychology, ch. 4. 
Prince, M., Dissociation of a Personality. 

Stoerring, G., Mental Pathology in its Relations to Normal Psychology 
(trans.), ch. 17. 



390 PERSONALITY 

Practical Exercises: 
Study the different phases of character of some former close friend. 
Analyze your temperament, and compare it with that of some intimate 

friend. 
Test children of different ages and one adult with the following Binet tests: 

repeating sentences of varying lengths; repeating numerals; definitions; 

memory from reading; naming as many words as possible; use of code. 

Compare results. 



CHAPTER XIX 
ORGANIZED MENTAL LIFE 

Mental Development. — In the last chapters (xi-xviii) we 
have examined the distinctive phenomena of central nervous 
activity, largely by the method of self -observation. The 
older investigators regarded these mental states and succes- 
sions of states as the typical subject-matter of psychology. 
Under our definition the scope of the science is broader. The 
central phenomena form but one fragment of the chain of 
events which occur in the mutual interaction between the 
environment and the organism. The specific type of inter- 
action which takes place by means of the nervous system and 
its adjuncts constitutes mental life, and the real subject- 
matter of psychology is the study of mental life as a whole. 

Mental states, attitudes, and character are phenomena of 
the central adjustment process. They are by far the most 
significant phenomena of mental life in its higher stages of 
development. Yet they represent only a cross-section of the 
entire chain of activity denoted by the term mental life. 

Viewed in its entirety, mental life includes all the activi- 
ties which enter into behavior. But even this conception is 
incomplete. The behavior phenomena undergo constant 
change in the history of each individual. Mental life is an 
evolutionary process — a growth. We can scarcely reach a 
full understanding of its higher manifestations unless we take 
into account the paths along which this development pro- 
ceeds. Broadly speaking, we find three lines of progress in 
mental life: 

Differentiation of mental states 
Mental organization 
Systematic control 



392 ORGANIZED MENTAL LIFE 

1. Differentiation. — The differentiation of mental states 
has been treated rather fully in preceding chapters.^ In ap- 
plying these results to organized mental life the point to em- 
phasize is the great qualitative variety of mental states. The 
vast number of different perceptions, feelings, etc., which we 
experience serve as basis for an endless differentiation of 
behavior. Central complexity is the immediate source 
of the complexity observed in the behavior of higher organ- 
isms. 

2. Mental Organization. — Every living being is an or- 
ganized system of material particles. The type of organiza- 
tion found in living biological beings is called the organic 
type; an organic imit is called an organism.^ 

The biological or organic type of organization, as we have 
seen (ch. ii), is exceedingly complex. A hving creature is able 
to maintain itself, repair structural damage within certain 
limits, increase its own size, and reproduce other beings like 
itself. All these functions are comprised in the notion of 
biological or organic life. An important feature of this type 
of organization is that the process of organization is self- 
operating. The activities of the cells and their components 
bring about structural differentiation and systematic organ- 
ization of the entire organism. The evolution and develop- 
ment of an organism is not due to the working of some outside 
agency, in the sense that a locomotive is constructed by men 
and by means of machinery, neither of which is part of itself. 

^ See chs. ix-xviii. 

^ The similarity of the two terms organism (adj. organic) and organization 
(adj. organized) is confusing. Organization means an arrangement of con- 
stituent parts in a system such that they work together and bring about 
systematic results. The Red Cross society is just as much an 'organization * 
in this technical sense as a human being. A locomotive or a printing-press 
may be regarded also as organized matter — as an organization. An organ- 
ism is one specific type of organization: that which has evolved among bio- 
logical units. It simply increases the confusion if we extend the connota- 
tion of organism, as some sociologists do, to include social organization. Even 
more undesirable would be its extension to human-made machines. 



MENTAL ORGANIZATION 393 

This distinctive feature of biological organization should be 
borne in mind when we consider mental organization. 

Mental organization rests upon a certain phase of the or- 
ganic organization — the nervous system and the terminal 
organs which are connected with it. This system forms the 
' structural basis ' of mental life (ch. iii). It is the ground- 
work of mental organization. The general make-up of the 
nervous system and terminal organs is the result of organic 
operations. The formation of neurons and their topographi- 
cal relations is an outcome of organic organization. To this 
extent mental organization is not a self-operating system. 

But when we study the system in actual operation we find 
that the inherited and developed nervous structure is not the 
only factor in mental organization. The interaction between 
the living creature and his environment is more than a ques- 
tion of specific nerve mechanism. In the higher species, and 
particularly in man, it depends essentially upon the organized 
mass of central experiences which have developed during the 
individual's life-time. Each separate experience modifies the 
nerve structure to some extent, and subsequent experiences 
are affected by the totality of these past modifications. 

When you manipulate your knife and fork at table, this 
response to the food stimuli is carried out in a certain specific 
way because of your many previous experiences of the same 
sort. You handle these implements differently than you 
would if your life had been spent in the backwoods, or in a 
savage community. You use them somewhat differently ac- 
cording as you have been brought up in America, France, 
Italy, or some other country. In this and other standardized 
forms of behavior, the mode of response to the specific stim- 
ulus has been molded through the operation of various stimuli 
— similar and dissimilar — in the past. These earlier stim- 
uli have altered the nerve mechanism little by little so that 
it responds in certain particular ways. 

In the two preceding chapters it has been shown that these 



m 



394 ORGANIZED MENTAL LIFE 

central modifications of the mechanism are not distinct and 
isolated. They affect one another and thereby develop 
general tendencies of behavior. The development of such 
tendencies is a process of organization. In this respect, men- 
tal organization constitutes a self-acting system. The system 
of interaction between the creature and his environment or- 
ganizes itself, within the limits of capacity provided by the 
inherited structural basis. 

Mental organization, then, depends upon both inherited 
nerve structure and the modifications which are wrought in 
that structure by use. The higher phases of mental life, such 
as language and rational activity, involve a long series of 
changes and integrations; these functions cannot be ade- 
quately described in terms of the original neural mechanism. 
The organization of experience is in large measure a func- 
tional process; it is perfected by its own operation. 

Mental organization differs in this from human-made 
machines. A locomotive or a sewing-machine may ' wear 
down ' somewhat through use, so that it works better after a 
time; but in the main the effects of use are destructive to 
human-made mechanisms. The mental mechanism on the 
other hand improves constantly through use, up to a certain 
final limit; its more complex achievements are attained only 
after a long process of functional development. 

Factors which Determine Mental Organization. — In the 
preceding chapter the term personality was used to denote the 
total manifestation of an individual's organization at any 
given stage. According to the older, static view of mental 
life, man's per-sonality was held to be wholly a product of 
heredity. The mind was considered an original endowment 
— something thrust full-fledged into the human body at the 
very beginning of the individual's separate existence. Growth 
and experience were supposed merely to remove the wrap- 
pings which concealed the true inner self and hampered its 
activity. The older psychology conceived of self or person- 



FACTORS IN MENTAL ORGANIZATION 395 

ality as fully formed at the outset and not subject to develop- 
ment. 

According to the evolutionary view, now generally ac- 
cepted, man's personality, like the specific phases of his men- 
tal life, is a real growth. The self starts as a rudiment with 
the first experiences of the embryo, and gradually increases 
in complexity. The growth of personality and individuality 
continues throughout life, and ceases only when death dis- 
integrates the nervous organization. "^ Personality is the 
result of progressive mental organization. Its specific mani- 
festations serve as an index of the degree and variety which 
that organization has attained at any period of life. 

Mental organization, as we have seen, is the joint product 
of two distinct factors: (1) the inherited neuro-terminal 
mechanism; (2) environmental forces which act upon this 
mechanism. The process of mental organization will be bet- 
ter understood, however, if we separate these into a number 
of more specific factors : 

Inherited structure 
Terminal organs and conducting neurons 
Central system 

Environmental and intra-organic forces 
Disorganizing influences 

Specific stimuli and general environmental conditions 
Social environment 
Educational influences 

(a) Terminal Organs and Conducting Neurons: The 
range of mental organization depends in large measure upon 
the variety and complexity of the receptors and effectors. 
A complex receptor organ, such as the eye, affords great pos- 
sibilities in the way of manifold different experiences. The 
various senses supplement one another and in their totality 
give vastly more complete data of the external world than 
any one of them taken separately. 

1 See Appendix, "Personal Immortality," p. 422. 



396 ORGANIZED MENTAL LIFE 

In the same way the multiplication of muscles affords op- 
portunity for coordinated expression and for adapting our 
responses to the external situation. The conducting paths, 
both sensory and motor, form an integral part of the receiving 
and responding mechanism. Without these paths the ter- 
minal organs would be isolated and would bear no direct 
relation to the unified mental life. 

(b) Central System : The fundamental factor in determin- 
ing mental organization is the central portion of the nervous 
system. An intricate system of neurons in the brain, and 
especially a highly developed cerebral cortex, gives opportu- 
nity for the growth of a high order of personality, while 
without this complex neural structure the range of a crea- 
ture's mental development is extremely limited. The general 
type of nervous system which characterizes any species is 
primarily the product of heredity, though its development in 
typical form in the individual depends to some extent upon 
environmental conditions, since neural growth may be 
thwarted by malnutrition and other influences. 

Man's superior mental organization is due chiefly to his 
inheritance of a highly complex cortical system, provided 
with a vast number of interconnecting neurons. Integration 
of stimuli, coordination of responses, and adjustment of re- 
sponse to stimulation all depend upon the central system and 
to a large extent upon the cortical tracts. These are all 
inherited structures. 

(c) Disorganizing Influences: The inherited mechanism 
of mental life is liable to be impaired in various ways by the 
action of outside forces. Our eyesight may be injured by 
overexposure to light or by some sharp body mutilating the 
eyeball. The loss of a foot or hand cripples our motor ex- 
pression. Injury to the brain by a fall or other 'accident ' often 
leads to serious disorganization of the adjustive functions. 

Degeneration and impairment of mental organization occur 
even more frequently as a result of forces within the body it- 



FACTORS IN MENTAL ORGANIZATION 397 

self. A tumor in the brain affects the structure or functioning 
of certain centers and this gives rise to pathological mental 
manifestations (aphasia, etc.). Malnutrition, disorders of 
digestion or other vital functions, use of narcotics, stimu- 
lants, and other poisons, alter the course of mental activity 
in various ways and affect character and personality corre- 
spondingly. Thomas Carlyle's pessimistic attitude is at- 
tributed to his dyspeptic condition. Diseases which destroy 
the tissues may affect the nerve substance or some of the re- 
ceptors or effectors. This disorganization occurs in varying 
degrees, from deafness following measles to paresis due to 
venereal infection. 

The most serious mental disorganization is due to condi- 
tions of permanent infection. Where parents are infected, 
this may modify, if not the germ cell itself, at least the em- 
bryonic development of the offspring. A large proportion of 
feeble-mindedness is attributable to this cause. Strictly 
speaking this is not inheritance, for the lack of mental devel- 
opment in such cases is not due to typical conditions in the 
germ cell. But it is an effect transmitted from parent to child, 
and on this account the retardation is often attributed to 
heredity. 

Mental pathology covers a broad field and forms a distinct 
branch of psychology — two branches in fact, for there is a 
wide distinction between mental retardation and mental dis- 
order (psychiatry). Each of these studies throws consider- 
able light on normal psychology. 

{d) Specific Stimuli and General Environmental Con- 
ditions: The direct and indirect effects of specific stimuli 
have been examined at length in earlier chapters. The 
systemic stimuli, so far as they lead to responses which modify 
the organism, broaden the sphere of mental life somewhat. Our 
responsive activities to internal pain, for instance, constitute 
an interrelation between the organism and itself — not be- 
tween creature aiid environment. Rubbing a bruised ankle. 



398 ORGANIZED MENTAL LIFE 

taking medicine to cure a digestive trouble, are reactions 
which adjust the conditions within the organism itself, and 
bear no significant relation to the external environment. 

General conditions of environment, such as climate and 
temperature, abundance or scarcity of food and material for 
protection and defense, play some part in determining mental 
organization; their influence is far less than that of specific 
situations. 

(e) Social Environment: The social environment or 
* social atmosphere ' is much more important in determining 
the higher stages of mental organization than stimuli from 
the ordinary physical environment. Language and the entire 
function of communication depend upon the presence of a 
social environment. It is reported that castaways show 
considerable retrogression in mental organization. Alexander 
Selkirk, whose solitary life for over four years on Juan Fer- 
nandez Island suggested the tale of Robinson Crusoe, lost 
much of his vocabulary and his facility to talk connectedly. 
Clear thinking is apt to be impaired by constant solitude, 
though alternation of solitary and social conditions often 
stimulates rational thought. 

The extent to which the development of mental life depends 
upon social influences in childhood is shown by certain in- 
stances of children brought up in solitude or apart from hu- 
man surroundings. In the case of Kaspar Hauser, who was 
apparently brought up almost without social intercourse, in- 
tellectual development was irremediably atrophied.^ Helen 
Keller, cut off from social stimuli through blindness and deaf- 
ness, made no progress in mental organization till taken in 
hand by an expert teacher. 

Social influences act both focally and marginally. Much 
of our mental growth in childhood is due to ' unconscious 
absorption ' of ideas and imitation of customs from those 

^ This may have been due to congenital factors, however. On the other 
band the legendary tales of Romulus and Mowgli are quite untrue to life. 



FACTORS IN MENTAL ORGANIZATION 399 

about us. Our mental organization is molded after the pat- 
tern of the community in which we live. An individual with 
a given heredity may become a notorious criminal or a power 
for good, according as he is placed in an unfavorable or 
favorable social environment. 

(f) Educational Influences: Education, in the sense of 
organized ' teaching,' constitutes a distinct factor in mental 
organization. It represents the dynamic influence of the 
social environment upon the individual. It is the systematic 
attempt of society to develop the mental organization of its 
members. 

Teaching occurs in a rudimentary form in primitive races, 
but its main significance is seen in the higher stages of civiliza- 
tion. Here it exerts a preponderating influence in organizing 
mental life. Beginning with home and church training it 
extends through the schools to the university and to technical 
institutions of every sort. By these means mental growth is 
'forced' — mental organization develops at a rate far exceed- 
ing that attained under passive social conditions. 

Heredity and Environment. — Comparing mental with 
* vital ' life, we observe a great contrast in the relative im- 
portance of heredity and environment as factors in promot- 
ing organization. In both cases heredity furnishes the essen- 
tial structural basis; but it determines the direction or trend 
of mental growth far less than that of general bodily growth. 

Biological growth demands of the environment only a 
certain gross uniformity of physical conditions (temperature, 
atmospheric density, etc.) and adequate nutriment. Indi- 
vidual differences in environmental conditions produce modi- 
fications of bodily growth, but these variations are relatively 
slight compared with the uniformities common to the species. 

In mental development, on the other hand, the individual 
variations due to environmental differences are enormous ^ — 

1 This would naturally be expected, since mental life depends upon inter- 
action with environment. 



400 ORGANIZED MENTAL LIFE 

particularly those due to the influence of social factors. Our 
mental heritage is chiefly an equipment which enables us to 
grow mentally. The direction actually taken by mental 
growth depends almost wholly upon social environment and 
education. The fullest organization of mental life is at- 
tained only when our inherited possibilities are utilized to the 
utmost through social imitation and training. 

Types of Mental Organization. — If we compare individual 
human beings we observe many striking differences in degree 
and type of mental development. The study of variations in 
degree of organization (mental level) carries us into the field 
of genetic psychology, a territory too broad for examination 
here.^ 

The subject of qualitative differences in mental organiza- 
tion belongs to ' general psychology ' to the extent that each 
type of personality represents the hypertrophy of some phase 
of mental life. 

On the receptive side notable differences in sensory mental 
type appear, which have been the subject of some experi- 
mental investigation. One man is found to be distinctfy 
' visual ' in type. In his case the visual data are habitually 
focalized and constitute the principal components in his men- 
tal states. He learns by reading better than by listening, his 
interest is in the microscope or in maps. If he is an author, 
his books abound in color terms and visual pictures. 

Another person is found to be auditory in type. He under- 
stands oral instructions readily, learns more easily from lec- 
tures than from text-books; he is quick at ' mental ' arithme- 
tic. His auditory imagery and in most cases his appreciation 
of music are unusually developed. 

A third belongs to the kinesthetic or motor type. With him 
language is primarily a motor phenomenon. His imagery is 
kinesthetic, he is apt at memorizing speeches, his interest is in 

^ One phase of the problem — intellectual growth — was touched upon 
in chapter xviii. 



TYPES OF MENTAL ORGANIZATION 401 

motor acts. The emphasis of his mental life is on the expres- 
sive side rather than the receptive. 

It is a mistake to assume that each individual belongs dis- 
tinctively to one of these types. In some cases the mental 
organization is rather evenly balanced. In many persons 
certain activities are preeminently of the visual type while 
others are based upon kinesthetic or auditory data. A man 
may be an ' auditory linguist ' in one tongue and a ' visual 
linguist ' in another. Apparently the only generalization 
justified so far by the study of sensory types is that most indi- 
viduals belong to a specific type in some degree and in respect 
to certain mental operations. 

A similar differentiation is observed in the organization of 
character. In certain individuals the intellectual side is over- 
developed, in others temperament, in others skill. How far 
these character types depend upon the prominence of elemen- 
tary components of the corresponding sorts in daily experi- 
ence is not yet known. The development of character types 
may be due primarily to inherited structural refinement of 
certain brain centers, or to unusually developed associative 
connections between certain centers. The results of experi- 
mental education demonstrate, however, that systematic 
training can at times direct the organization into definite 
types or smooth out certain prominences of type to a very 
considerable degree. 

3. Control. — The third line of progress in mental life is 
control. We may distinguish between several phases of 
control: ^ 

Control of responses 
Control of environment 
Self-control 
Social control 



1 The types of control treated in chapters xiv and xv depend upon differ- 
ences in the mechanism by which adaptation is brought about. The phases 
discussed here differ in the sphere in which the adaptation occurs. 




402 ORGANIZED MENTAL LIFE 

(a) Control of Responses: The central adjustment of 
nerve impulses through experience tends to make the indi- 
vidual's motor activities continually more suited to the situ- 
ation. The learning process (which is central adjustment) 
enables the creature to protect himself and gain food with less 
expenditure of energy and with fewer failures. There is a pro- 
gressive improvement in his motor coordination. The indi- 
vidual gradually achieves control of his own movements. This 
is the fundamental aspect of control. 

(6) Control of Environment: A higher stage is reached 
when the environment itself is more or less permanently modi- 
fied by our responsive activities in such a way as to assist our 
life processes. When primitive man prepared skins of ani- 
mals and used them to clothe and protect himself, he ad- 
vanced one step toward control of his environment. The mak- 
ing of forest trails, building of huts, sowing of fields, and do- 
mestication of animals are other early instances of man's 
active influences upon the physical world. In civilized man 
ships, railroads, harvesters, lighting plants, and all the prod- 
ucts of industry may be regarded as instruments or means 
for the control of nature. 

The key to this higher growth of control is found in the 
complex central process which one observes in himself as 
volition. We have noticed (ch. xiv) the tendency of volun- 
tary expression to conform to the ideational factors in the 
experience. When the central mechanism is so developed 
that our images and thoughts lead to corresponding forms of 
activity, the way is open to control of the environment. The 
complex results attained in this direction by civilized man are 
due to a cumulative training of thought and volition. The 
highest attainments involve nothing psychologically new, 
except the social factor. Control of the external world is 
aided by social example and teaching, and more especially by 
the permanent graphic records which broaden the scope of 
man's social environment and preserve the acquisitions of 
each generation for use in future ages. 



CONTROL 403 

(c) Self-control : Development of control along a dis- 
tinctly, different line occurs when man learns to inhibit or 
modify his own systemic and motor processes. This is illus- 
trated in repression of the emotions and less obviously in 
a systematic regulation of one's daily work. Here the signifi- 
cant result is not so much the alteration of environment as 
systematic direction of phenomena within the body. The 
term self-control is commonly applied to the inhibitive side of 
this process, but it may well be broadened to include the guid- 
ance and active alteration of mental operations. 

The attainments of civilized man in this field are as notable 
as his control over nature. He is not only ' master of his fate ' 
but ' captain of his soul.' The sphere of psychology is ex- 
tended to include not merely the reaction of the creature upon 
the environment, but his reaction upon his own bodily and 
mental organization as well. 

{d) Social Control: Still another line of development is 
social control.^ ^ By means of language and other communica- 
tive expression human beings are able to guide the actions of 
their fellows and of lower animals. Here we have two stand- 
points to consider — that of the controller and the controlled. 
To the active agent in the social relation the results are not 
essentially unlike those attained in controlling his physical 
environment. But from the standpoint of the individual 
affected the phenomenon presents certain new features. 

Mental organization may be either promoted or impeded to 
a large degree by social control. The process of teaching is 
one phase of the phenomenon, and a most useful one. Psy- 
chotherapy, the improvement of bodily and neural conditions 
by suggestion from others, is another phase, which covers a 
wide field. " Inspiration by example " is still another in- 
stance. On the other hand, one individual may come so 

1 The term is used by sociologists to include government and other organ- 
ized social agencies. In general psychology it means control of one organism 
by another. 



404 ORGANIZED MENTAL LIFE 

under the domination of another that his mental develop- 
ment is seriously thwarted. The slave and the professional 
hypnotic subject illustrate this deleterious working of social 
control. The result here is mental deterioration instead of 
evolution. 

Personal Control and Personality. — The development of 
control depends upon the progressive organization of central 
adjustment. Every response, however complex, is deter- 
mined by present stimuli and by the alterations which the 
resulting impulses undergo before they lead to motor expres- 
sion. The significant alterations of nerve impulses are those 
which occur in the central region by way of summation, dis- 
tribution, retention, and metabolic change, with resulting 
modification. These central alterations of impulses become 
systematized step by step with the organization of mental 
life. The systematic modification of central impulses gives 
rise to the various types of mental states and attitudes noticed 
in previous chapters. The final product of ce;itral organiza- 
tion is 'personality, which includes all these varieties of con- 
scious experience. 

If now we regard organized mental life as behavior, we can 
trace the results of its progressive organization in the various 
types of control just discussed. The final outcome from this 
standpoint is personal control, which represents the interwork- 
ing of all the specific phases. 

Speaking in terms of behavior, mental organization means 
the progressive coordination of responses, and their adjust- 
ment to the whole group of stimuli which affect the organism. 
In the earliest stage, behavior consists in isolated respolises to 
isolated stimuli. Through evolution and individual develop- 
ment these separate activities gradually become unified. The 
final stage in the organization of behavior is personal control 
of the total situation. 



GENERAL SUMMARY 405 

General Summary of the Book 

Psychology, as defined in the beginning of the book, is the 
scientific description and explanation of mental life, which de- 
notes a type of process by which the environment affects the 
organic being and the organic being in turn affects the envi- 
ronment. The distinctive feature of this type of interaction 
is that it is mediated through the operation of a special mech- 
anism known as the neuro-terminal system (ch. i). Accord- 
ingly as an essential basis for our study of mental life, we 
examined the general characteristics of organic beings or 
organisms (ch. ii) and the structure of the neuro-terminal 
system (ch. iii). 

The elementary unit of the nervous system is the neuron. 
The activity of neurons is probably a chemical change which 
is propagated along the nerve fiber, accompanied by electrical 
disturbance. We noticed seven properties or distinguishable 
operations of neural activity: excitation, conduction, reten- 
tion, metabolic variation, summation, distribution, and modi- 
fication (ch. iv). As noted further on, these characters are 
observed in our own subjective experience as impression, 
suggestion, revival, vividness, combination, discrimination, 
and transformation (ch. viii). 

The individual neurons are built up into a complex system 
of arcs, each arc consisting of three parts, the sensory, central, 
and motor segments, which are joined to form a circuit, the 
sensory end being connected with a special terminal organ 
called the receptor, and the motor end with another special 
organ called the effector. The operation of the nervous arc 
consists in the transmission of an impulse from end to end. 

A nerve impulse starts with stimulation of some receptor 

by a force from outside the nervous system.^ The effect is 

transmitted directly to a neighboring sensory neuron and 

arouses a nerve impulse, which is transmitted successively 

^ Not always froxxi. outside the body. 



406 GENERAL SUMMARY 

through the sensory, central, and motor segments of the arc. 
The motor impulse ultimately causes activity in some effector 
organ, which produces a ' motor effect ' upon the environment 
or upon the inner mechanism of the body. This final motor 
effect is called the response. 

The significant part of the chain of neural activity is the 
operation of the central section of the arc, which integrates 
impulses from various sensory paths, and coordinates im- 
pulses passing into various motor paths. This central opera- 
tion is called adjustment; it brings about responses which are 
more or less ' fit ' or ' adapted ' to the specific situation in 
which the organism is placed. The entire chain of processes 
in the circuit (stimulation — adjustment — response) taken 
together constitute behavior (ch. v.). 

Mental life in the broadest sense is behavior. We examined 
the operation of behavior as a whole, taking up first the sim- 
pler types, reflex and instinctive behavior (ch. vi) and then the 
complex form called intelligent behavior (ch. vii). 

In studying intelligence we found that the complex proc- 
esses in the central section of the arc are the essential fea- 
ture of the operation. These processes are not at present 
open to examination by objective methods; we examined 
them by the subjective method of self-observation. 

The elementary data which make up our conscious experi- 
ences are of two sorts: sensations and ideas. Sensations are 
the original, primary components of experience. They arise 
directly from stimulation. Ideas are secondary or derivative 
data. They are not the direct result of stimulation, but arise 
in the brain and are due to the retention in some central 
neuron of the effects of past experiences. An idea may be 
regarded as the ' second edition ' of a sensation (ch. viii). 

Sensations are classed according to the type of receptor 
which arouses them. Eleven different senses are distin- 
guished. We examined each of these in turn (ch. ix, x). 

The sensory data fall into three classes: external, systemic, 



GENERAL SUMMARY 407 

and motor, from which typically different sorts of experience 
arise. In all, four distinct kinds of components are distin- 
guishable — the three varieties of sensory data and a single 
class of ideational data. The elementary components are not 
experienced separately in adult life; our experiences are com- 
binations and transformations of these data (ch. xi). 

A specific experience is called a mental state. Mental states 
may be classed as primary and secondary. Primary mental 
states are those in which some one "\^ariety of data predomi- 
nates. They are classed as perceptions, imagery, feelings, 
and conations. A perception is a mental state in which ex- 
ternal sensations predominate (ch, xii). In imagery the idea- 
tional data due to external sensations predominate. Imagery 
includes several distinct sorts: memory images, free images, 
anticipation images, imagination images, and general images. 
A feeling is a state in which systemic sensations are dominant. 
In conations the motor (especially kinesthetic) sensations 
predominate (ch. xiii). 

Secondary mental states are those in which two or more 
different sorts of data are prominent. They are classed as 
emotions, sentiments, volitions, thought and language, and 
ideals and rational actions. In emotions both systemic and 
kinesthetic data are prominent; in sentiments ideational 
and systemic data; in volition ideational and kinesthetic data 
(ch. xiv). 

In thought and language the original ideational and kines- 
thetic data are transformed into new and higher complex states 
through the social interrelations of individuals. A distinc- 
tive feature in thought and language is the verbal symbol. 
Ideals and rational actions are mental states in which all types 
of data except external sensations are prominent (ch. xv). 

Mental life consists of a succession and transformation of 
mental states of these several sorts. The succession of per- 
ceptions depends largely upon environmental conditions; it is 
due to the serial order of the external stimuli affecting our 



408 GENERAL SUMMARY 

receptors. Successions of imagery and thought, on the other 
hand, depend primarily upon central conditions; one idea 
succeeds another as the impulse is modified in passing from 
one central neuron to another, each with its own character- 
istic retention set. The general stream of experiences which 
constitutes our conscious mental life includes both types of 
succession. Mental states of every sort combine and succeed 
one another as a result of changing external and internal 
conditions (ch. xvi). 

When similar experiences occur repeatedly they tend to 
produce a general retention effect in the brain centers. A 
general set of this sort is called an attitude. There are several 
different kinds of attitudes; the most important are interest, 
desire, attention, dispositions, appreciation, and conscience. 
Each of these is based upon one of the fundamental types of 
mental states (ch. xvii). 

Through repeated experiences, specific attitudes of each 
sort combine to form general attitudes, which constitute the 
character of the individual. The most prominent phases of 
character are temperament, intellectuality, skill, and morality. 

The several phases of character, taken together, make up 
the general character of the individual, called his 'personality 
or self. Personality is the product of our heritage and of our 
entire past life (ch. xviii). 

The mental life of each individual is constantly developing. 
Its growth is seen in the progressive differentiation of mental 
states and in the advance of mental organization and control. 

Mental organization is the joint product of the inherited 
neuro-terminal mechanism and the environmental forces 
which act upon this mechanism. The cortical areas are the 
most important structural factors in determining its progress; 
social forces, especially the operation of systematic education, 
are the chief functional factors. 

The growth of control follows several lines. It consists first 
of all in gaining control of our own bodily movements. In its 



GENERAL SUMMARY 409 

higher stages it results in control of the environment, self- 
control, and social control. The interworking of these phases 
results in personal control. This is the final outcome of or- 
ganized behavior, just as personality is the final outcome of 
central organization or organized conscious experience. Per- 
sonal control means that the individual himself is master of 
the situation in which he lives (ch. xix). 

Special Conclusions. — We may emphasize in closing 
some of the more important facts regarding mental life which 
the book has aimed to bring out. 

(1) The mental life of man and other creatures depends 
upon the presence of an inherited neural mechanism. Every 
conscious experience is accompanied by activity of the nerv- 
ous system. Conscious experiences, or mental states, may 
be regarded as the subjective aspect of nerve activity. The 
complexity and effectiveness of these neural processes de- 
pend upon the degree of structural organization of the in- 
herited neuro-terminal system. In man this system is highly 
organized; it is derived jointly from two parents and is due in 
part to each. 

(2) Mental life depends also upon the presence of an active 
environment which operates upon the neuro-terminal system 
through the process called stimulation. The data which 
enter into experience are derived either directly or indirectly 
from stimuli outside the body, the internal stimuli being 
traceable ultimately to previous external stimulation. In man 
the social environment is an important factor in developing 
the higher phases of mental life. 

(3) Mental life depends, accordingly, upon the interaction 
of a creature and his environment by means of a neuro-terminal 
system. Mental activity may be regarded as the stimulative 
effect of the environment upon the creature, with the resulting 
responsive effect of the creature upon the environment 
brought about by neural processes. 

(4) Each specific manifestation of mental life may be stud- 



410 GENERAL SUMMARY 

ied as a sequence of stimulation, adjustment, and response; 
this chain of processes constitutes behavior. The most im- 
portant factor in behavior is the adjustment process; this may 
be studied by the human individual through observation of 
his own experiences. Self -observation is examination of the 
central adjustment phenomena as mental states, or conscious 
experiences. 

(5) The types of mental states found in man are a gradual 
growth. Even our attitudes, character, and personality un- 
dergo development during our life-time. They are not im- 
planted at birth, but are formed by degrees. While the men- 
tal states which appear in the adult human individual may be 
investigated separately as static phenomena, the organiza- 
tion of mental life which produces them can only be ade- 
quately explained in genetic terms. Mental organization 
develops gradually in each individual; its structural basis has 
evolved step by step in race history. 

(6) The evolution of every structure and of each type of 
process concerned in mental life depends upon its utility. In 
order to survive, an organism must be adapted to its environ- 
ment. Like every other biological product the neural mech- 
anism, by whose operation experiences are organized, is be- 
lieved to have arisen originally through some chance varia- 
tion — that is, through some new combination of factors in 
the germ cells. The persistence of the new structure is due 
to the fact that the individuals which possess it are more 
fitted to survive than those in which it is lacking. The same 
is true of the various forms of experience. The higher types 
of mental states (such as thought and language) which have 
grown up and established themselves in the human species, 
have arisen and persisted because they proved useful in 
mediating between man and his environment. 



SPECIAL CONCLUSIONS 411 

Collateral Reading: 

Conklin, E. G., Heredity and Environment, ch. 6, and Introduction (De- 
velopment of the Mind). 
Hobhouse, L. T., Mind in Evolution (2d ed.), chs. 1, 18, 19. 
Yerkes, R. M., Introduction to Psychology, chs. 30-32. 
Ingenieros, J., Principios de psicologia biologica, chs. 6, 7. 
Crampton, H. E., Doctrine of Evolution, ch. 6. 
Thorndike, E. L., Educational Psychology (briefer course), ch. 27. 
Angell, J. R., Chapters from Modern Psychology. 

Practical Exercises: 

Analyze how far your personality appears to be due to heredity and how far 
to yoiu" social environment. 

What is your present idea of ' a mind ' ? 

Describe observed instances of the growth of control in various phases of 
mental life — emotional display, sketching, systematic study, moral 
conduct; if possible take your own case in one of these instances. 



APPENDIX 

Some of the underlying principles assumed in psychology 
are still under debate. The results obtained up to the present 
are not thoroughly conclusive, and scientific investigators 
disagree in interpreting the facts. It is not possible within 
the limits of a text-book to discuss the merits of the conflicting 
interpretations. In this book the solution which appears 
most promising has been indicated in each case, with a foot- 
note referring to the Appendix, 

The debatable problems are discussed here for the benefit 
of advanced students. The aim is not so much to " settle the 
question," as to point out where the difficulty lies and why a 
certain answer has been adopted in the text. Arguments for 
opposing views will be found in the references. -. 

PROBLEM I 

THE MIND-BODY RELATION 

Subjective and Objective Phenomena. — Since the time of 
Descartes considerable emphasis has been laid upon the dis- 
tinction between mind and matt^.' Philosophers and scien- 
tists have been impressed with the "dual nature of being." 
As Descartes himself expressed it, being has two distinct 
modes : thought and extension. This notion has led to the be- 
lief, widely held, that there are two substances in the universe, 
a mental substance and a material substance. Even if this 
belief were universally accepted (which it is not), the problem 
of the ultimate nature of these substances need not trouble 
the scientist. For every science finds some elemental datum 
which it assumes without attempting to explain. 

But the psychologist is confronted with another problem in 



414 APPENDIX: MIND-BODY RELATION 

this connection, which cannot be so easily dismissed. All 
experience shows a certain relation between mental (subjec- 
tive) phenomena and material (objective) phenomena. Ap- 
parently this is not a symmetrical relation. Many material 
or physical events occur which are not related to any discov- 
erable events in conscious experience; but our conscious ex- 
periences are all associated with certain physical events. The 
physical events which accompany mental states are activities 
of the nerves and of the receptor and effector organs. Unless 
we decide at the outset to surround our science of psychology 
with an impenetrable Chinese Wall separating bodily activity 
from conscious experience, we find it expedient to adopt some 
working hypothesis which will account for their observed 
relation. 

Recent psychology for the most part is divided between 
two conflicting interpretations of the relation between mental 
and physical phenomena. These hypotheses are called In- 
teractionism and Parallelism. Both assume that subjective 
and objective phenomena are distinct classes of events. fM 

According to the Interaction hypothesis physical events ' 
cause mental events, and conversely mental events cause phy- 
sical changes. In other words, the two series are not simul- 
taneous, but an event in one series produces the correlated 
event in the other. Brain activity causes thought; thought 
in turn produces activity in the brain. In support of this 
view are cited the effectiveness of conscious purpose and the 
selective character of the human will; also the persistence and 
evolution of consciousness in the animal series, which indi- 
cates that it plays an effective role in organic life. 

The hypothesis of Psychophysical Parallelism differs from 
Interactionism in assuming that the correlated events in the 
two series occur simultaneously. According to this view the 
series of mental states runs parallel with the series of nerve 
impulses. Thought accompanies brain activity. The two 
series are in one-to-one relation, but they constitute distinct 



SUBJECTIVE AND OBJECTIVE PHENOMENA 415 

phenomena. This interpretation is believed by its advocates 
to accord better with current theories of the persistence of 
force and conservation of energy than the Interaction hy- 
pothesis. 

A third view, often confused with Parallehsm, is the 
Double- As'pect hypothesis, which is adopted in the present 
book. This view has the support of several well-known psy- 
chologists (e.g., Fechner, Titchener) and is perhaps actually 
held by others who call themselves Parallelists. The Double- 
Aspect interpretation differs from both Interactionism and 
Parallelism in assuming that conscious and neural phenom- 
ena constitute one single series of events, and that their 
different appearance is merely due to different ways of ob- 
serving them. When they " happen to me " they appear 
as conscious experiences; when I observe them indirectly, 
through perceiving the behavior of other beings by means of 
my senses, they appear in the form of motion, chemical 
change, and the like. 

According to this hypothesis consciousness ' belongs to ' the 
activity of neurons as truly as the intensity or form of neural 
impulses belongs to this same activity. Just as in physics, 
when we discuss the properties of masses we find correlated 
phenomena, such as surface relations, which may or may not 
be studied but belong to the same group of phenomena, so in 
biology when we examine the properties of nerve substance we 
observe certain correlated phenomena called conscious experi- 
ences. They form part of the ' total description' of nerve 
activity. In physics the same event or group of events may 
be studied through several different manifestations: we ob- 
serve increase in heat through rise of mercury in a bulb or 
through the fusing of some metal. Neural events, according 
to the Double-Aspect hypothesis, are likewise observable 
either as behavior or as ' our own ' experiences. 

The Double-Aspect hypothesis is adopted here because it 
does not clash with observed facts and because it seems to 



416 APPENDIX: MIND-BODY RELATION 

provide the best working tool for psychological investigation, 
It enables us to bring the results of objective and subjective 
observation into cooperation — using our physiological and 
behavior material to bridge the gaps in conscious experience, 
and using the results of self -observation to supply the miss- 
ing data of brain activity. 

Parallelism divides the organic world into two independent 
sets of events, which go on simultaneously and correspond- 
ingly but are entirely distinct from each other. There is a 
suggestion of ' preestablished harmony ' between the two sets 
which seems to require explanation. The Interaction theory 
would fill this demand effectually if it really 'worked.' But 
so far no satisfactory statement has been formulated to de- 
scribe how neural events act upon consciousness, nor how con- 
scious states work upon the nervous system. The argument 
for Interactionism, so far as it is based upon the phenomena 
of Volition and Purpose, seems to rest upon incomplete or 
faulty observation and analysis of these phenomena. 

It should be remembered that the whole problem is stiU 
under discussion. Each of the three theories mentioned has 
a respectable following; the student must choose for himself 
among them. Whichever interpretation he adopts should 
be treated merely as a working hypothesis, subject to revision 
if a better explanation can be found. 

Perception of the External World. — The term introspec- 
tion is commonly used to denote observation of our own con- 
scious experiences. The word is confusing, for it seems to 
imply turning our inspection ' inward,' either to the organic 
feelings which originate within our body or to the images 
which are localized in the brain centers. Even the term self- 
observation is open to this misconstruction if we emphasize 
the word 'self.' Self -observation means observing the effects 
of external stimuli quite as much as observing the internal 
components of our experiences. As a matter of fact everything 
that " happens to me " is material for my self-observation. 



PERCEPTION OF THE EXTERNAL WORLD 417 

There is a real problem connected with external self-obser- 
vation which perplexes the student of psychology. How is it 
that the same events are at once experiences and objective 
phenomena ? How can the same thing be a book outside my 
body and something which I experience as blue, oblong, thick, 
heavy? A consistent interpretation of the facts is by no 
means easy. Various hypotheses have been proposed to ex- 
plain the relation of the perceiving individual to the perceived 
object.^ 

A solution of the difficulty is suggested by the double-aspect 
hypothesis, though many psychologists do not regard it as a 
satisfactory interpretation of the facts. The world about us 
consists of electrons, grouped into atoms, molecules, cells, and 
organisms. These objects stimulate our receptors either by 
direct contact or by means of waves and emanations. The 
effect of stimulation is carried by our sensory nerves to the 
brain. When the effect occurs in your own brain it is your 
experience. What we experience immediately, then, is not 
the trees, houses, books, men, etc., situated in the outer world 
beyond the body, but the cerebral effects of stimulation by 
these objects. The outer world is brought in to us — we do 
not go forth and explore it.^ 

The point to emphasize is the cerebral location of perceptual 
experience. Whatever illusions and distortions occur in per- 
ception are due to defects in the transmission process, anom- 
alies in grouping the material, or other central factors. 

But how comes it that the things which we perceive appear 
to us to lie outside of our body and often at a distance? The 
answer seems to hinge upon the ' projection ' operation, which 
is one of the varieties of transformation that the sensory data 
undergo. The experience of ' extended space ' is just as 

^ In philosophy this is called the problem, of knowledge, or epistcmology. 

2 When we hear a friend's voice over the telephone the vocal characteris- 
tics are conveyed through a long circuit in form of electric waves, finally 
reaching our car. Yet we are undoubtedly "hearing his voice." The case 
of neural transmission is analogous. 



n^ 



418 APPENDIX: MIND-BODY RELATION 

much experience as the quality 'red ' or the quality 'sweet '; 
in each case the character of the experience corresponds to a 
character of the stimulus. The two are congruent though they 
may not resemble each other. 

After all, perception of objects as situated at a distance 
from us simply means that the data stand in certain space re- 
lations to the visual, tactile, and kinesthetic perceptions of our 
body; the sensory data from our body and other objects pass 
through the same neural paths and are combined in percep- 
tual experiences. An argument for this interpretation is 
found in stereoscopic perception. Here the data are two flat 
photographic pictures, slightly different from each other. 
When we observe them under proper conditions they are 
perceived as a single 'solid' object, projected considerably 
beyond the actual plane of the photographs. 

Thought-Transf erence ; Psychical Research. — A question 
of considerable importance for psychology is whether organ- 
ism and environment can interact in a mental way without 
the medium of the sensory and motor conducting systems. 
This problem is not necessarily bound up with that of the re- 
lation between consciousness and the nervous system (inter- 
actionism). Even under the parallelistic and double-aspect 
interpretations it is legitimate to inquire whether the central 
nervous mechanism and the environment do not at times in- 
teract by other means than through the sensory and motor 
nerves. 

In this as in all scientific problems what we have to do is to 
collect data and weigh the evidence. Two questions of fact 
are involved in the problem of thought-transference : 

(1) Does the brain (or consciousness) receive impressions 
from the outer world directly? This issue is called Telepathy. 

(2) Is the brain capable of producing changes in the outer 
world directly? This is the issue of Telekinesis. 

Telepathy has been far more carefully studied than Tele- 
kinesis. The investigations deal chiefly with social data —^ 



THOUGHT-TRANSFERENCE 419 

the supposed transfer of thoughts from one person to another 
through non -nervous channels. 

The Societies for Psychical Research have examined and 
reported a host of instances in which individuals have appar- 
ently received information from a distance by means which 
preclude the hypothesis of ordinary sensory communication. 
A man reports that he dreamed of his mother's death at the 
precise instant when the event occurred; or he claims to have 
had a haunting thought of the event in waking life. Clair- 
voyants demonstrate their apparent ability to read messages 
blindfold, to describe an object lying in a distant room, to 
tell what one is thinking about, etc. Such reports, collected 
by sincere and imimpeachable scientists, fill volumes of the 
Proceedings of these societies. Psychologists are not agreed 
as to whether these occurrences are actually telepathic. 
William James was a staunch supporter of psychical research 
investigations; but so far as known he never definitely ex- 
pressed either belief or disbelief in the telepathic character of 
the phenomena. Contemporary American psychologists for 
the most part reject the telepathic interpretation. 

In this book the phenomena are not treated, because the 
collected e\ddence does not appear to substantiate the claim 
that they are due to direct thought-transference. Many of 
the phenomena reported may be explained according to well- 
known mental and physical processes; the residue may prob- 
ably be attributed to these also. The arguments against the 
acceptance of the telepathic hypothesis are as follows: 

(1) Faulty Memory: In many cases the temporal coinci- 
dence has proved on investigation to be faulty. The thought 
of a friend's death may have occurred some time before or 
after the event. In course of time we forget the discrepancy 
and come to believe that the two events coincided. 

(2) Chance Coincidence : The statistics are weighted in 
one direction. If a premonition of death coincides closely 
with the event, it is remembered and reported; if not, it is 



420 APPENDIX: MIND-BODY RELATION 

forgotten. The strongest premonition the present writer 
ever had was in 1900, when he felt sure a cable would an- 
nounce the death of a near relative. The person in question 
is still alive and hearty. If all such negative cases were re- 
ported the ratio of fulfillments to total cases might not 
exceed the theory of chances. The element of * reasonable 
expectation ' also impairs the evidential value of certain coin- 
cidences; if a friend is seriously ill we are not unlikely to 
have thoughts of his death. 

(3) Collusion and Fraud: The experimental investiga- 
tions of clairvoyance are not open to either of the above ob- 
jections. But in many cases it has been shown, either that 
information is given to the ' percipient ' by some accomplice 
through ordinary sense channels, or that the percipient him- 
self used sensory means, such as seeing under the blindfold, 
exchanging one envelope for another, etc. 

Even among naturally honest folk there is a strong tempta- 
tion to secure striking results. One important set of tests 
reported in good faith by the Psychical Research Society 
were afterwards shown to involve collusion between the per- 
cipient and her sister. The writer confesses to having been a 
confederate during his college days in some parlor ' experi- 
ments ' which for a time convinced a large group of class- 
mates who were not in the conspiracy. How far this explana- 
tion may be applied to serious investigations is a delicate 
question. The sincerity of the Psychical Research scientists 
is above suspicion ; but the good faith of their human material 
is not always to be relied upon — neither is it by any means 
certain that the investigators are acquainted with all possible 
varieties of deception. Every new fraud and every new 
means of deception discovered casts additional doubt on the 
validity of the phenomena. 

(4) Unobserved Sensory Impulses :' Thought is ordinarily 
due to sensory impulses; but these impulses are transformed 
into new modes. When we are reading, the separate printed 



THOUGHT-TRANSFERENCE 421 

characters are rarely observed. At times whole sentences are 
not observed as printed words : the stimuli are transformed at 
once into images and thoughts. 

There are many ways in whichour thoughts may be shaped 
and molded by sensory indications so faint that another per- 
son fails to observe them, even though he tries his level best 
to pick up every clue. In certain states of hyperesthesia the 
patient is able to distinguish one blank page from another 
through microscopic differences in texture. Slight ' imper- 
ceptible ' adjustments of the vocal organs which accompany 
thought may be correctly interpreted by the percipient. Al- 
terations in breathing, minute ' attitude ' expressions may be 
read by a trained observer. In every-day life we often ' feel 
the tenseness ' of the social environment or ' open up ' in a 
more congenial atmosphere, though the distinguishing marks 
of the situation are too indefinable to be described in language. 
The operation of such subliminal factors in directing our 
thoughts is far more common than is ordinarily realized. In 
many cases it seems quite possible to explain the phenomena 
in question by these unobserved sensory data without assum- 
ing telepathic communication. 

(5) The Trend of Evolution: The world of organisms has 
built up a tremendously complex mechanism consisting of 
receptors, sensory nerve-paths, and centers, whose function is 
to convey and integrate impressions from the outer world. 
This mechanism has evolved slowly in race history, presum- 
ably by chance variation and natural selection. If some 
simpler means of conveyance is available, as claimed, it seems 
highly probable that at some point in the course of history a 
systematic mechanism for this would have been perfected and 
become a dominant factor in mental life. In other words, the 
fact that a complex nerve mechanism has evolved everywhere 
among the higher species is presumption against the existence 
of the simpler receptive mechanism involved in telepathy. 

Telekinesis, the supposed production of motion in objects 



422 APPENDIX: MINDBODY RELATION 

outside the body by mere volition, has not been so exten- 
sively investigated as the opposite phase of thought-trans- 
ference. If by telekinesis is meant causing motion in masses 
of inorganic matter, the phenomenon is open to more rigid 
experimental tests today than telepathy. A few instances 
have been reported by scientific observers in which a physical 
object (such as a balance) has moved up or down apparently 
at the will or thought of the observer without muscular action 
on his part. 

These results have not been accepted by physicists gener- 
ally. It has been suggested that they involve faulty observa- 
tion. It is important that the tests be repeated under rigid 
experimental conditions by many independent investigators. 
Only in this way will the validity of the telekinetic hypothesis 
be definitely proved or disproved.^ 

Personal Immortality. — The question whether human 
personality survives death and organic dissolution has en- 
gaged the attention of thinkers since the dawn of science. It 
is in fact a problem of more than theoretical interest. The 
persistence of our personal identity beyond the span of our 
life-time is a factor of some practical importance in formulat- 
ing our career and determining our program of conduct. 

The problem is germane to psychology, yet it is avoided in 
most recent text-books. The reason for this attitude is easily 
stated. Psychology in its present stage of development af- 
fords no real indication of the answer to be given. There is 
no direct evidence of personal survival in the phenomena of 
mental life. Certain analogies indeed may be cited for an 
affirmative view. It is possible, also, that the finer traces of 
mental organization persist after the gross organization of 
the body has become disintegrated. On the other hand hu- 

^ Recently some experiments upon telepathy by the use of laboratory 
apparatus have been undertaken at Harvard and elsewhere. The results of 
such experiments, carried out under carefully controlled conditions, should 
be far more evidential of the truth (or falsity) of the hypothesis than vol- 
umes of mediumistic phenomena. 



PERSONAL IMMORTALITY 423 

man personality now appears to be closely bound up with an 
organization consisting of many neurons, and the interrelation 
of the separate neurons is lost at death. 

Numerous instances of supposed communication with the 
dead have been collected by the Societies for Psychical Re- 
search; but for the most part their validity is open to doubt. 
The messages reported do not indicate a high level of mental 
organization, such as in many cases their reputed authors 
possessed in life. 

Possibly future investigations either in psychology proper 
or in the field of psychical research will furnish conclusive, 
or at least satisfactory evidence. At present, scientific psy- 
chology neither affirms nor denies personal immortality. 

References 

(1) Subjective and Objective Phenomena; Perception of the External World: 
McDougall, W., Body and Mind, chs. 6-26 (esp. ch. 26). 
Villa, G., Contemporary Psychology, ch. 3. 
James, W., Principles of Psychology, chs. 5, 6. 
Holt, Marvin, and others, The New Realism. 
Ladd and Woodworth, Physiological Psychology, Part III. 
Fechner, G. Th., Zendavesta, II, sec. 19D. 
Titchener, E. B., Text-Book of Psychology, sees. 3, 4. 
Warren, H. C, The Mental and the Physical, Psychol. Rev., 1914, 2i, 

79-100. 
Bowne, B. P., Introduction to Psychological Theory, Part II, ch. 4. 
ChfFord, W. K., Lectures and Essays, Vol. II, ' Mind and Body.' 
Holt, E. B., The Concept of Consciousness. 
Baldwin, J. M., Development and Evolution, ch. 1. 
Morgan, C. L., Instinct and Experience, ch. 8. 
Parmelee, M., Science of Human Behavior, ch. 16. 
Uexkiill, J. v., Umwelt und Innenwelt der Tiere; last chapter. 
Verworn, M., Die Mechanik des Geisteslebens. 
Claparede, E., La psychologic comparee est-elle legitime ? Arch, de 

psychoL, 1906, 5, 13-35. 
Russell, B., Scientific Method in Philosophy; esp. chs. 3, 4. 
Forel, A., Hygiene of Nerves and Mind in Health and Disease, ch. 3. 
(2) Psychical Research: 

Barrett, W. F., Psychical Research (and literature there cited). 
Abbott, D. P., Behind the Scenes with the Mediums. 
Hyslop, J. H., Borderland of Psychical Research. 



424 APPENDIX: MIND-BODY RELATION 

Podmore, F., Apparitions and Thought-transference. 
Crookes, Wm., Proc. Soc. Psychical Research, Vol. 6, pp. 98-127,, 
Coover, J. E., Experiments in Psychical Research. 
Crawford, W. J., The Reality of Psychic Phenomena. 
(3) Personal Immortality: 

Lodge, O., The Survival of Man. 
Hyslop, J. H., Science and a Future Life. 
James, W., Human Immortality. 



PROBLEM II 

MECHANISM AND PURPOSE 

Purpose in Organic Growth. — The phenomena of growth 
and regeneration in organisms are strikingly imique. A 
creature of any given species develops from a fairly simple 
cell to a complex, differentiated organism which resembles 
the other organisms of that species both as a whole and part 
by part. In the lower species and in the earlier stages of em- 
bryonic growth, if a portion of the body be cut away (by acci- 
dent or experimentally) the missing part is restored and the 
new growth is similar to the original. Both " growth to 
type " and " restoration to type " are processes quite different 
from anything observed in the inorganic realm. They are 
activities apparently guided toward bringing about certain 
future results. 

The question therefore arises: Is the apparent guidance of 
organic growth due to a specific kind of force, different in sort 
from physical and chemical forces — a force or agent which 
operates only within living organisms? Certain biologists 
believe this to be the case. They point to the fact that the 
vital processes ' look ahead ' — that the successive stages in 
gi'owth are means to an end, — whereas inorganic processes 
are merely transformations of prior conditions. This hypoth- 
esis is called Vitalism. The great majority of contemporary 
biologists, on the other hand, believe that the forces which 
operate in organic growth are merely complex manifestations 
of the same physical and chemical processes which operate 
throughout the inorganic world. This hypothesis is known 
as Mechanism. 

The processes which occur in growth are still in course of 
investigation. The direct e\adence at present favors the 



426 APPENDIX: MECHANISM AND PURPOSE 

mechanistic contention: all the physiological processes so far 
observed are chemical and physical in character. But the 
results are as yet very incomplete and do not justify a final 
conclusion. 

The difficulty is two-fold: (1) The growth processes are so 
complicated that we can only observe them piecemeal. We 
cannot marshal the eiltire array of cooperating factors which 
produce mitosis and enlargement in individual cells and inter- 
action between cells. (2) The investigations have been con- 
ducted wholly along physical and chemical lines, so that it is 
to be expected that they would bring to light only physical 
and chemical factors. Hence, unless we chance to stumble 
upon some inexplicable result, they would afford us no evi- 
dence of the presence of a vital force. 

On the other hand it should be remembered that the Vital- 
ists have not succeeded in formulating any definite description 
of the character or workings of the supposed * vital force.' 
It is a general maxim of science to explain the imknown in 
terms of the known, and so far this principle has always 
proved correct. We do not assume a special type of force in 
the motions of the planets ; they are explained in terms of grav- 
ity, like the fall of bodies toward the earth. In the present in- 
stance both this general maxim and the weight of empirical 
evidence point to the mechanistic interpretation of growth 
and the other vital processes. The demonstration is not con- 
clusive, since a crucial test is still lacking. But the burden of 
proof seems to rest with the Vitalists to demonstrate the ac- 
tual existence of a specific type of force in vital phenomena. 

The apparently ' purposive ' character of growth may be ex- 
plained without assuming the agency of a guiding force if we 
interpret the individual life of organisms in terms of their race 
history. 

The chain of reasoning on which this interpretation rests is 
as follows : In the evolution of species each new organ or modi- 
fication of an organ is assumed to have appeared originally as 



PURPOSE IN ORGANIC GROWTH 427 

a chance variation. Many such variations have occurred in 
successive generations — some beneficial, some detrimental, 
some neutral. Detrimental and beneficial variations are 
equally ' probable. ' But detrimental variations hamper their 
possessors in their competition with others of the species to 
secure food or protection from enemies, while beneficial vari- 
ations render their possessors better able to secure food or 
escape danger. Thus the possessors of new favorable varia- 
tions are more likely to attain maturity and produce many 
descendants. The beneficial form of organ accordingly tends 
to spread more and more among the species, while the less 
favorable types tend to disappear. 

The variations which count in evolution are those based 
upon alterations in the germ cell. No modification of other 
cells affects the offspring; characters acquired after birth may 
help or hinder the individual himself, but they are not trans- 
mitted to succeeding generations. 

Now to apply this to individual history. The whole course 
of a creature's growth is mapped out by the constitution of 
the germ cell from which he originates. The constitution of 
any individual germ cell is the result of variations which have 
occurred one after another in past generations. The varia- 
tions which have persisted and are now found in this particular 
germ cell are consequently not of the average hit-or-miss sort 
- they are such as have proved their utility by surviving. In 
a word, individual growth is purposive (in the sense of meet- 
ing the future circumstances of the creature), not because it is 
controlled by a guiding force, but because the constitution of 
the germ cell which determines growth has been subjected to 
a selective process. 

Conscious Purpose. — The behavior of organisms exhibits 
' future reference ' to a more marked degree than their vital 
processes. This characteristic is manifested in both instinc- 
tive and intelligent responses, but is most clearly observed in 
the conscious experiences of human beings. We ' look 



428 APPENDIX: MECHANISM AND PURPOSE 

ahead ' and plan our actions with a view to bringing about 
some definite result. The future outcome is already foreseen 
in thought. Such experience is called conscious purpose. The 
pictured result is called an end, the intermediate actions are 
termed means, and the initial mental state is a forethought or 
purposive thought. 

The fact that we are able to picture future situations is 
deemed by some psychologists to constitute a distinguishing 
mark of conscious behavior. This conscious component is 
supposed to differentiate intelligent from non-intelligent acts. 
Purposive thought, like other types of thought, leads to motor 
activity; and if the ability to pictm*e the future is solely a 
character of consciousness, it follows that consciousness is 
itself a factor in determining the course of activity. In other 
words, according to this view consciousness is not merely a 
characteristic of neural activity; but it is a force or guiding 
activity in itself. This interpretation of purposive activity 
is called Voluntarism, since it emphasizes in peculiar fashion 
the volitional type of experience.^ 

Voluntarism is generally associated with the Interaction 
interpretation of the mind-body relation. It assumes that 
mental activity is something distinct from neural activity. 
The mind attains its forethoughts, and indeed its whole grasp 
of the ' situation,' by certain specific processes of its own, 
utilizing the data furnished by the senses merely as a basis. 
It then initiates a course of action — conscious purposive 
action — which produces material results radically different 
from any which could otherwise be attained. 

Opposed to this interpretation is the view that purposive 
behavior proceeds along substantially the same lines as other 
types of behavior — that it is fully determined by neural ac- 
tivity, and that all the transformations involved in the chain 
of events may be expressed in terms of physical and chemical 

^ There are several variations of the hypothesis which emphasize other 
types of experience. 



CONSCIOUS PURPOSE 429 

processes. This interpretation, which may be called Psy- 
chological Mechanism, has been adopted in the present book. 
The following arguments may be mentioned in its favor: 

A large part of the difficulty in explaining purposive activ- 
ity is due to the extreme complexity of the phenomena in- 
volved. The Voluntarists assume that this complexity im- 
plies a radically new type of behavior. But complexity only 
means that the phenomena in question are difficult to analyze. 
It affords no real ground for assuming novelty of constitution. 
In spite of this complexity it is possible to analyze purposive 
behavior into simpler and more familiar phenomena. We can 
trace its sources to two well-known features of the nervous 
mechanism: distant sensation and retention. 

Perception combines data from the distant senses with 
those from the contiguous senses. We see a ball coming 
toward us before it strikes our body. The response may be to 
the distant stimulus alone, or to the contiguous stimulus 
alone, or to their combination. If the ball strikes us heavily 
and gives rise to pain, we react to the pain stimulus. But the 
whole series of stimuli leave retention traces in the cortical 
centers. The next time a ball comes toward us the visual 
stimulus may arouse memory images of the entire succession 
of events ; the memory of the former blow may arise before the 
ball reaches us, and we then react to the enlarged situation, 
which comprises the distant ball and the previous pain. Ow- 
ing to the uniformity of nature, our responses to such situa- 
tions tend to become suitable to the course of events. We 
dodge the ball, or we catch it in our hands. The 'purpose 
image, then, is based upon a memory image aroused by distant- 
sense data; the fitness of the ensuing course of action is due 
to the uniformity of nature. 

Simple types of purposive behavior are observed among 
animals. When a dog chases a rabbit the locomotor activity 
is part of the feeding response, though it precedes the dog's 
contact with his prey. More than this, as Perry points out, 



430 APPENDIX: MECHANISM AND PURPOSE 

the salivary and gastric processes in the dog begin while he 
is still chasing the rabbit. All these activities are purposive; 
the response begins before the total situation is 'presented through 
the receptors ; — it is anticipatory. 

In all such cases there is central integration and adjust- 
ment. The anticipation image is a mental state as well as a 
complex motor impulse. The Psychological Mechanist dif- 
fers from the Voluntarist chiefly in his interpretation of the 
causal relation between the central and motor phenomena. 
The Voluntarist. regards the animal's consciousness as a sepa- 
rate factor in the determination of action; the Mechanist 
believes that the whole sequence of physiological changes 
may be expressed in terms of physical and chemical processes 
— that in all purposive behavior the entire series of physical 
events follows the " line of least physical resistance." 

Space will not allow us to follow out here the development 
of purposive activity into its higher complexities. It is a far 
cry from catching a ball to planning one's whole life career. 
The Psychological Mechanist is hampered by the intricacy of 
the factors ; but he believes that by patient research they will 
eventually be isolated and shown to be merely complications 
of the same physical and chemical processes which make up 
simple purposive action. 

In accounting for behavior, as in solving the problem of 
growth, the burden of proof seems to rest upon those who 
would introduce a novel process. Voluntarism is called upon 
to give an understandable account of the new force which 
it assumes. This it has not succeeded in doing up to the 
present. 

Psychological Mechanism does not minimize the impor- 
tance of consciousness in life nor its value in scientific research. 
According to the mechanistic interpretation, however, con- 
sciousness is not an active /orce, capable of producing changes. 
It is rather a characteristic of certain natural events; — a 
datum to be taken into accoimt in scientific investigation and 



CONSCIOUS PURPOSE 431 

apparently capable of furnishing valuable indications regard- 
ing cerebral processes and mental life generally.^ 

Free-Will, Determinism, and Responsibility. — The Vol- 
untaristic hypothesis usually carries with it the view that 
voluntary acts are not fully determined by stimuli, nerve 
structure, and past experience. Given the situation as pre- 
sented to the conscious individual by these three factors, a 
man is nevertheless ' free ' to decide upon his course of action 
and to direct his movements accordingly. This interpretation 
of conscious behavior is called Free- Will or Indeterminism. 
According to the Indeterminist, at certain points in the se- 
quence of events the course of physical motion or chemical 
changes in the brain is not an exact resultant of the material 
forces which are operating; certain physiological processes are 
checked (inhibited) or their direction is altered by ' conscious 
determination.' If the Interaction view be adopted there is 
nothing self -contradictory or absurd in this conclusion. Con- 
scious processes, if independent of physiological processes, 
may certainly follow different ' laws ' from the latter. The 
balance of probabilities, however, seems to favor the opposite 
interpretation — Determinism. 

(1) There are countless demonstrations of the conservation 
of energy. The physical law that motion follows the line of 
least resistance has been verified so far as careful research has 
been able to test it. 

(2) The actual workings of volition are capable of being ex- 
plained according to physical and chemical principles so far 
as their intricacy permits the analysis. 

(3) Even though at times we are conscious that we deter- 
mine our acts independently of the situation, social statistics 

^ A third alternative interpretation of the facts is Behaviorism, which 
swings to the other extreme. The Behaviorist contends that the data of 
consciousness should be ruled out of science altogether because they are not 
causal factors. This narrowing of the scope of science has not justified itself 
up to the present. Self-observation has proved more useful than the study 
of behavior in investigating the phenomena of human mental life. 



432 APPENDIX: MECHANISM AND PURPOSE 

indicate that in the aggregate such acts really follow the lines 
marked out by conditions of heredity and environment. 
Crime and benevolence, taken in the aggregate, vary as func- 
tions of the social milieu and biological inheritance of the 
group. Even suicide fluctuates with community conditions. 

One reason given by many for adopting the Indeterministic 
view is that ' free-will ' affords the most satisfactory basis for 
moral responsibility. For if a man's actions are completely 
determined by his heredity and his environment, how can he 
be ' held responsible ' for what he does ? 

Stated in this form the problem lies beyond the sphere of 
psychological investigation. But the psychologist may prop- 
erly ask: What does ethics mean by ' moral responsibility ' 
and ' holding a man responsible '? ^ If a man's heritage 
and training do not measure his degree of responsibility, what 
does? Are his responsible acts determined by pure chance? 

A favorite interpretation of modern Indeterminists is that 
the determining factor (outside of heredity and environment) 
is not chance, but ' personality.' Here we return to psycho- 
logical territory again. Psychology traces the growing com- 
plexity of life from elementary sensations to complex mental 
states and attitudes; a man's character and personality appear 
as the outcome, the culmination, of his past mental life. 
Personality is the result of environing forces working con- 
stantly upon an inherited mechanism. Thus we are brought 
to the Deterministic interpretation unless we identify respon- 
sibility with random decision — unless responsible acts are 
haphazard events. 

The science of ethics appears to require some reinterpreta- 
tion to adjust it to the results of modem psychological re- 
search. The older conception of moral responsibility in par- 
ticular seems to need revision. Responsibility, after all, may 

^ Legally, an imbecile or an insane man is not held responsible for his acts. 
An animal is not morally responsible. A human child is held only partly re- 
sponsible. On the other hand no amount of adverse environmental influences 
absolve a man from responsibility in the eyes of the law. 



FREE-WILL, DETERMINISM, RESPONSIBILITY 433 

be not so much a basis for unfriendly recrimination and judi- 
cial retribution. It may be rather the measure of a man's 
mental level, of the degree of organization which his adjust- 
ive mechanism has attained. 

Personification of Natural Phenomena. — In the course of 
this discussion we have noticed several hypotheses which at 
one stage or another run counter to a thoroughgoing mech- 
anistic interpretation of nature. They assume that at some 
point or points in history new data appear or a new kind of 
force manifests itself. 

Some of the supposed new forces or data concern psycholo- 
gists only indirectly. But the theories may be classed 
together because they typify a general tendency of scientific 
thought — a tendency which manifests itself most noticeably 
in the earlier stages of every science. Primitive science 'per- 
sonifies complex phenomena; it treats certain of them as 
directing agents in the course of events. 

In physics and chemistry these personal agencies have been 
gradually discarded. In biology the complex phenomenon of 
life is still hypostasized by the Vitalists. Similarly in the 
domain of mental phenomena will, thought, and 'personality 
are hypostasized by certain psychologists as determiners of 
activity. There is also a type of psychology which considers 
consciousness and intelligence as generators of movements, 
rather than as characters of phenomena, like beauty or trans- 
parency. 

The Mechanist finds such explanations unsatisfactory be- 
cause they do not attempt to show how these personal agencies 
operate. To say that vital force causes growth, that intelli- 
gence or will causes muscular movement, does not indicate 
the manner in which the physical changes involved in growth 
or muscular movement are effected. It merely gives a con- 
venient name to the process. 

In the old magic, pronouncing some word, such as "Abra- 
cadabra," was supposed to bring about tremendous results. 



434 APPENDIX: MECHANISM AND PURPOSE 

It was never explained how the sound vibrations operated. 
In fact, the mystery of the process was especially emphasized. 
The Mechanist sees a similar mystical tendency in modern 
personificatory interpretations of nature. 

The underlying assumption of a 'personal agency' may 
prove correct in one form or another. But the trend of 
scientific progress is all in the other direction. As our know- 
ledge of natural phenomena advances these personal agencies 
are one by one resolved into physical and chemical operations 
of the phenomena themselves. The evidence today seems 
clearly to favor the Mechanistic interpretation as a working 
hypothesis in psychology as in other fields of science. 

References 

(1) Purpose in Organic Growth (Vitalism vs. Mechanism) : 

Loeb, J., The Organism as a Whole. 

Loeb, J., The Mechanistic Conception of Life. 

McDougall, W., Body and Mind. 

Driesch, H., The History and Theory of Vitalism. 

Driesch, H., The Problem of Individuality. 

Henderson, L. J., The Fitness of the Environment. 

Henderson, L. J., The Order of Nature. 

Haldane, J. S., Mechanism, Life, and Personality. 

Henderson, Jennings, and others. Articles in Philos. Rev., 1918 (Nov.), 
27. 

Baetschli, O., Mechanismus und Vitalismus. 

Roux, W., Problems, Methods, and Scope of Developmental Me- 
chanics (trans.). 

Le Dantec, F., Traite de biologic, ch. 13. 

Bibliography in J. of Philos., 1918, 15, pp. 550-553. 

(2) Conscious Pm-pose, and Free- Will: 

Hobhouse, L. T., Development and Purpose. 

Wundt, W., Grundziigederphysiologischen Psychologic (5th ed.) ch. 21. 

Russell, B., Scientific Method in Philosophy, ch. 8. 

Watson, J. B., Psychology as the Behaviorist Views it, Psychol. Rev., 

1913, 20, 158-177. 
Warren, H. C, The Mechanics of Intelligence, Philos. Rev., 1917, 26. 
Warren, H. C, A Study of Purpose, J. of Philos., 1916, 13. 
Perry, R. B., Docility and Purposiveness, Psychol. Rev., 1918, 2$, 1-20. 
Conklin, E. G., Heredity and Environment, ch. 6. 

(3) Personification: 

Comte, A., Cours de philosophic positive. Vol. I, Lesson 1. 



PROBLEM ni 

NEURAL ACTIVITY 

Nature and Modal Variation of the Nerve Impulse. — It 
has long been known that some sort of electric phenomenon 
accompanies the transmission of the nerve impulse. This is 
clearly indicated by fluctuations which are observed in the 
galvanometer needle during the process. It has naturally led 
to the assumption that neural conduction is primarily an 
electric phenomenon. Recently it has been found that a 
chemical change also takes place in the nerve fiber during the 
activity caused by stimulation. The amount of carbon diox- 
ide is increased in the active nerve to about double that of the 
resting nerve. When the activity ceases the over-supply of 
CO2 is eliminated. 

On these grounds Herrick thinks it probable that "the trans- 
mission of a nervous impulse involves a wave of chemical 
change throughout the length of the nerve fiber, though a 
change of a quite different character from that occurring in 
the cell body during its functional activity " of nutrition and 
growth (Introd. to Neurol, p. 97).^ At present, then, we 
may regard the nerve impulse as a ' chemo-electric ' phenom- 
enon, with greater stress laid, perhaps, on the chemical side. 

It may strike the student as extraordinary that the nature 
of so patent a phenomenon as the nerve impulse should still be 
in doubt. One reason is that the neurons are surrounded by 
other tissue, and that it is difficult to separate them from the 
surrounding mass without functional disturbance. The ex- 

1 The slow rate of nerve conduction has also been urged as an argument 
against regarding the phenomenon as a simple electric discharge. But the 
varying rate of electric transmission in core conductors renders this argument 
questionable. 



436 APPENDIX: NEURAL ACTIVITY 

periments in nerve conduction have generally been performed 
upon excised nerve and we cannot judge whether the artificial 
stimulation used in this work produces a genuine nerve im- 
pulse. In these experiments electrical stimulation is em- 
ployed and the observed effects are electrical. No means 
have been found to determine what other processes are going 
on in the fiber except the very slight chemical changes recently 
discovered. The interpretation of neural activity has for 
these reasons been based largely upon the analogy of electrical 
phenomena. 

Many physiologists assume that the sensory nerve impulse 
varies in one ' dimension ' only; they recognize variations in 
intensity, but not variations in kind or mode. They attribute 
the variety in the effects to combinations of impulses in dif- 
ferent paths which meet at common synapses and spread 
along divergent paths again. 

In opposition to this view the modal differentiation of the 
nerve impulse is adopted ia the present book, for the following 
reasons : 

(1) Many transmission phenomena which occur in nature 
vary in two independent ways. This is noticed especially in 
undulatory motion. Sound waves vary in rate as well as 
amplitude; the same is true of light waves. The nerve im- 
pulse may well be analogous to these types of transmission. 

(2) The central effects of nerve impulses, observed as sensa- 
tions, differ in quality as well as intensity. These cortical 
phenomena are the direct result of stimulation. Thus at one 
end of the series there are differences in rate (e.g., among visual 
stimuli), at the other end differences in quality (among visual 
sensations). It seems highly probable, then, that the inter- 
mediate processes (impulses in the optic nerve) vary in a 
corresponding way. This species of variation, which is inde- 
pendent of intensity (amplitude), is what we mean by mode. 

How far this interpretation is correct can only be deter- 
mined by more thorough research into nerve physiology. 



I 



NATURE AND MODAL VARIATION 437 

Assuming its truth, it affords a simple and intelligible explana- 
tion of our conscious experiences. 

Retention, Metabolism, and Modification. — The phe- 
nomena of retention and recall have been noted since the be- 
ginning of psychological observation. Aristotle, in his scien- 
tific treatises, discussed recollection and formulated some of 
its principles. In modern times, since the fundamental im- 
portance of the nervous system in mental life came to be 
recognized, the problem has been to discover the nature of 
the effect which remains over in the nervous system, and how 
this after-effect operates to bring about the phenomenon of 
revival. 

We are still at sea as to the nature of neural retention. If 
little is known as to the character of the nerve impulse, still 
less has been discovered about the effect remaining after its 
passage. Direct investigation has revealed nothing so far; we 
know beyond peradventure that some effect is retained, and 
that is about all. The retention effect is probably not in the 
cell body, whose function is apparently concerned with 
growth and nutrition of the neuron; it is therefore some 
change either in the cell fiber, or at the synapse, or both. 

Contemporary investigators tend to place the ' seat ' of 
retention at the synapse. What is retained, according to 
this view, is the permeability of a given synapse due to the 
passage of an impulse, and an increase of permeability after 
repeated passages across the same synapse. Recall is ex- 
plained as the subsequent passage of impulses over the same 
group of synapses. The course of the totality of impulses 
through the cortical paths at a given instant is interpreted 
as involving adjustment and balance of many synaptic resist- 
ances in all paths of the central field. 

According to the hypothesis adopted in this book, the 
synaptic resistance and permeability is only part of the story. 
Another and more important factor in retention is some sort 
of trace or set left in the fiber itself, due to the mode of the 



438 APPENDIX: NEURAL ACTIVITY 

impulse which has affected it. Since our hypothesis calls for 
two factors (set of the nerve fiber and synaptic resistance), it 
is less simple than the other view, which explains the phe- 
nomenon in terms of a single factor — synaptic resistance. 
It therefore requires justification; the burden of proof rests 
upon its advocates, according to the canons of science. 

The reason for preferring the less simple interpretation in 
this particular case is that retention is subject to two influ- 
ences, fatigue and habit, which work in opposite ways. 

(1) Certain metabolic changes in the body outside of the 
nervous system affect neural activity. They are largely kata- 
bolic, and impair the function of neural activity. In this case 
impairment, or ' fatigue,' is the positive phenomenon; ' restor- 
ation ' is merely recovery from the effects of fatigue. 

(2) Retention of the effects of previous excitation is a phe- 
nomenon of the opposite sort. Repetition strengthens the 
retention. Here improvement of connection is the positive 
phenomenon; lapse of time and intervention of other neural 
happenings merely lessen the retention effect. 

Inasmuch then as we have two counterworking types of 
effect to deal with, we are justified in assuming two distinct 
types of operation to produce these effects. The fatigue 
process probably occurs at the synapses, since elsewhere the 
neurons are protected (insulated) from external influence. 
The retention process, on the other hand, is closely bound up 
with neural activity and may be effective either at the synap- 
ses or in the nerve fibers. 

Now if we adopt the modal hypothesis (for reasons given 
above), it seems likely that various modes of impulse produce 
different effects in their passage through neurons, and these 
effects not improbably leave a trace or set of some sort in the 
neural substance. In physics we observe a set in certain 
bodies remaining as an after-effect of forces acting upon them. 
A violin sounding-board becomes attuned to certain vibra- 
tions if played constantly by a master in the same standard 



RETENTION, METABOLISM, MODIFICATION 439 

of pitch. The receding tide leaves ridges in the sand which 
vary according to the size of the waves. Many analogies of 
various sorts indicate the likelihood of some lasting impres- 
sion in the nerve substance as a result of conduction — im- 
pressions which assume a specific form if the same mode of 
impulse passes through the nerve repeatedly. 

This interpretation of retention would explain why the op- 
tic region always affords visual sensations, even when stim- 
ulated electrically or by other non- visual activities. It ex- 
plains the resemblance of the memory image to the original 
sensation. It enables us to understand also the occurrence of 
ideation in general. A ' deep ' trace in a central neuron would 
tend to alter the mode of any impulse entering it, so that the 
mode of an impulse is in many cases modified into the mode 
of the retention trace. 

The laws of association may be readily interpreted under 
this hypothesis in neural terms. An impulse passes more 
easily into a neuron which is partly ' attuned ' to its mode — 
that is, into one whose retention set is similar to the mode of 
the present impulse. It is a question not merely of the rela- 
tive permeability of the several discharging synapses from a 
given neuron, but also of similarity between (a) the set in the 
neurons beyond the branch-points and (6) the mode of present 
impulse. 

The complexity of our perceptions and thoughts, and the 
new qualities which characterize many such complex experi- 
ences, find an explanation in the modal hypothesis. In many 
physical processes the combination of two or more different 
factors produces a complex effect. Two simple sound waves 
or light waves unite to form a complex vibration. We may 
assume, similarly, that when many nerve impulses of various 
modes gather together in a single central neuron, the resulting 
impulse (and trace) in that neuron will be correspondingly 
complex. 

It is observed also in certain physical phenomena that the 



440 APPENDIX: NEURAL ACTIVITY 

rhythm, rate, or other character of a process becomes altered 
by the continued operation of extraneous forces upon it. The 
sounding-board which has been attuned to certain vibratioas 
may gradually acquire a new ' set ' if the standard pitch of the 
instrument is slightly raised or lowered. We may assume in 
like manner that the set of a neuron is gradually altered by 
the passage through it of impulses which are characterized by 
other modes than its own. This character of neural activity 
was treated in chapter iv under the name of modification. 

The modification of the complex set of a neuron is assumed 
to be the basis of the new qualities observed in imagery and 
thought. It explains in part the variety of subjective experi- 
ence. It also accounts for the specific qualities of thought 
and the wide gap which appears between the fundamental 
types of ideational experiences (imagery) and the higher types 
of symbolic ideation (thought). In 'imageless thought' the 
set of the given neuron or neurons is so completely modified 
that the transformed experience has lost all resemblance to 
its original source. 

It should be emphasized that this view of neural activity is 
adopted only as a working hypothesis. The modal interpre- 
tation appears to meet the facts more satisfactorily than any 
other so far suggested. The problem remains quite open, 
however, pending direct evidence from physiological inves- 
tigation. 

References 

Herrick, C. J., Introduction to Neurology, esp. ch. 6. 

Lucas, K., Conduction of the Nervous Impulse. 

Sherrington, C. S., Integrative Action of the Nervous System. 

Ladd and Woodworth, Elements of Physiological Psychology, Part I,, 

chs. 5, 11. 
Semon, R., Die Mneme. 

Washburn, M. F., Movement and Mental Imagery, esp. chs. 3, 5, 6, 10. 
Schaefer, E. A., Text-Book of Physiology, art. "Nerve," pp. 451-560. 
Bayliss, W. M., Principles of General Physiology, ch. 15. 
Starling, E. H., Principles of Human Physiology, ch. 6. 
Tashiro, S. A., A Chemical Sign of Life. 



PROBLEM IV 

THE VISUAL PROCESS 

Principal Facts. — Like the nerve impulse, the visual 
process is apparently open to very precise experimental in- 
vestigation. The facts are so obvious that it would seem a a 
easy matter to explain them. The diflBculty lies in the variety 
of phenomena presented and the apparent irreconcilability of 
certain facts with certain others. The visual process is a sort 
of Chinese puzzle, whose parts certainly can be fitted together, 
but which has not yet been completely solved. 

The visual data (hues, shades, color-shades, and tints) de- 
pend primarily upon the rate and intensity of the physical 
light waves which stimulate the rods and cones of the retina. 
When we vary the stimuli in various ways, introduce varia- 
tions of general illumination, alternate different stimuli, stim- 
ulate contiguous areas of the retina, etc., certain peculiar 
results are observed in the sensation. The problem is to 
discover a physiological process of such a nature that it will 
produce all the results actually observed. So far every theory 
proposed fails at one or more points. At least one piece in 
our Chinese puzzle is always left over. 

The principal facts to be explained are given in Table 
XXIII. The theories proposed to account for the visual 
process have generally been based on certain of these facts 
and have found difficulty in explaining others. 

Three-Color Theories. — The oldest modern theory, called 
the Young-Helmholtz Theory, was proposed by Thomas 
Young and amplified by Hermann von Helmholtz. It is 
based upon the three ' fundamental ' colors (4).^ Since all 
color hues can be produced by appropriate mixtures of a 
1 These numbers refer to the facts hsted in the Table. 



442 APPENDIX: THE VISUAL PROCESS 

Table XXIII. — Visual Phenomena 

A. Relations among Colors: 

1. Hues at the two ends of spectrum (R and V)i are similar. 

2. Purple is a simple visual impression, though not a spectral hue. 

S. Mixture of two neighboring hues gives a simple intermediate hue (e.g., 
R-[-Y=0). 

4. Any hue may be obtained from mixtures of three fundamental hues, 
R, G, and B. 

5. There are four distinct primal hues, R, Y, G, and B. 

B. General Relations of Colors to Grays: 

6. Mixture of any hue with a certain other hue (called its complementary) 
produces gray. 

7. Mixture of all spectral hues together produces gray. 

C. Special Relations of Colors to Grays: 

Gray sensation, not color, is produced 

8. by color stimuli oi faint intensity; 

9. by color stimuli affecting a small retinal area; 

10. by color stimuli affecting the periphery of the retina. 

11. Certain color stimuli produce gray, not color, in color-blind individuals. 

D. Complementary Relations of Colors and of Grays: 

12. Fatigue leads to complementary after-effects on the same retinal area 
(e.g., B gives Y, Bk gives W). 

13. Complementary contrast effects appear simultaneously on neighboring 
areas under certain conditions. 

E. Miscellaneous Relations: 

14. Absence of stimulation on a portion of the retina may yield a sensa- 
tion (Black) on that area. 

15. Under varying illumination the relative brightness of -colors may vary 

(Purkinje phenomenon) . 

' In the table and following discussion the spectral colors are designated by initials : 
R=red, etc. Also 'W= white, Bk = black. 

certain R, G, and B (or R, G, and V) it was assumed that the 
cones of the retina comprise three distinct substances, and 
that each cone is suppHed by three nerve fibers of distinct 
sorts. ^ Thus a red light- wave would stimulate the red-sen- 
sitive substance; this would excite an impulse in the red- 
conducting fiber and produce the sensation Red. And so for 



THREE-COLOR THEORIES 443 

G and B. Intermediate hues (including Y) would stimulate 
two of the substances. Stimulation of all three substances in 
equal degree produces the sensation W. 

This theory was modified when research failed to reveal 
three distinct substances in the retina; and three distinct sorts 
of process were assumed instead. The Young-Helmholtz 
Theory with its modifications constitutes a group of Three- 
Color theories. The Three-Color theories explain facts 1 to 4 
in the list. They were indeed devised especially to meet these 
facts. They are also based upon 7, and they readily account 
for 6. Peripheral gray (10) may be explained by the absence 
of cones in the peripheral region. Color-blindness (11) may be 
explained as due to some structural defect, such as absence of 
one of the three substances, or to conditions which destroy the 
basis for one of the processes. The fatigue complementary (12) 
is due to exhaustion of one component. The Purkinje phe- 
nomenon (15) may be explained by assuming that the three 
substances (or processes) follow different quantitative laws. 

The remaining facts do not readily square with this type of 
theory. Y does not resemble R or G any more than G re- 
sembles B, or B resembles R. How then explain the primal 
character of Y (fact 5) ? Facts 8 and 9 seem to directly con- 
tradict the theory. For when only a small area is affected by 
a color stimulus one would expect a very distinct color impres- 
sion to occur, rather than gray ; and when the stimulus is faint 
one would expect (if anything) less tendency to gray sensation 
than to the specific color. The simultaneous contrast-color 
effect (13) is the most troublesome fact to account for on the 
Three-Color basis. Helmholtz explained it by assuming that 
it is not a peripheral phenomenon at all; he regarded it as a 
cerebral phenomenon — a mental judgment. The same ex- 
planation is used to account for Black (14). 

Metabolic Theories. — A distinct type of theory, based 
upon the antagonistic processes of anabolism and katabolism, 
was proposed by Ewald Hering to meet these difficulties. 



444 APPENDIX: THE VISUAL PROCESS 

Several modifications of Hering's views are generally grouped 
together as Antagonistic-Process or Metabolic theories. 
These theories are based primarily upon facts 5, 6, 13, 14. 
They assume three different pairs of metabolic processes in 
the retina. Each pair consists of two antagonistic ^ proc- 
esses — one anabolic, the other katabolic. In the first pair 
the anabolic process furnishes the sensation G, the katabolic 
R; in the second the anabolic gives B, the katabolic Y; in the 
third, which is more wide-spread than either of the others, 
the anabolic process gives Bk, the katabolic W. Note that 
the R, Y, and W sensations resemble one another and are in 
marked contrast with G, B, and Bk; the former group are 
'warm' colors, the latter 'cold.' The several processes were 
first attributed by Hering to three distinct substances in the 
retina, but inasmuch as appropriate substances were not to 
be found, they were later assumed to be distinct sorts of 
chemical action in the retina. 

The Metabolic theories account especially well for the four 
primal colors (5) and for Black (14). They explain facts 1 
to 3, mixtures (6, 7), and the fatigue complementary (12) 
as plausibly as the Three-Color view; they have the merit of 
accounting for the small-area (9) and faint-stimulus (8) phe- 
nomena, which play havoc with Three-Color theories gener- 
ally. The phenomenon of peripheral gray (10) is accounted 
for by assuming that both the B — Y and G — R processes are 
lacking at the periphery, while color-blindness (11) is attrib- 
uted to the entire lack of one (or both) of these processes in 
the retina of certain individuals. The Purkinje phenomenon 
(15) may be readily understood by assuming quantitative dif- 
ferences between the B — Y and G — R processes. An advan- 
tage of this type of theory is its explanation of simultaneous 
contrast (13) as a retinal process. Any given visual process 
in one area of the retina, it is assumed, tends to draw the req- 
uisite chemical elements from the surrounding regions, which 

* Greenwood suggests that these be more appropriately called opposite 
processes. 



METABOLIC THEORIES 445 

serves to arouse the antagonistic process in these neighbor- 
ing parts; this would also explain Bk — W contrast (13), which 
presents considerable difficulty to the Three-Color theories. 

The Metabolic theories do not attempt to explain how all 
hues can be obtained from mixtures of three ' fundamental ' 
colors (4). This is not a serious difficulty; yet one sees no 
reason why one primal color (Y) should be so much less funda- 
mental than the other three. According to this type of theory 
the sensations B, G, and Bk are the result of anabolic proc- 
esses; whereas in other receptor fields only katabolic proc- 
esses give rise to nerve impulses. It is further objected that 
whereas in two of the pairs (Y — B, R — G) the antagonistic 
processes when they occur simultaneously are supposed to 
neutralize each other, in the third pair the simultaneous oc- 
currence of the antagonistic processes yields Gray, a sensation 
which resembles one member of the pair (W). None of these 
objections strikes a vital blow at the Metabolic interpreta- 
tion. They merely give an impression of incompleteness or 
lameness in the explanation. 

The weightiest objection to this type of theory is the em- 
pirica,l fact that the members of one pair, primal R and 
primal G, do not actually neutralize each other as the hypo- 
thesis requires they should. The four specific colors selected 
as primal have been determined empirically; they are pro- 
duced by certain wave lengths which yield the same quality 
of sensation with no variation of hue as the stimulus passes 
from fovea to periphery. The fact that one pair does not 
meet the basal condition of the theory (complete opposition) 
seems sufficient reason for seeking a radical revision. 

Genetic Theory. — The Ladd-Franklin theory is described 
in chapter ix. It supposes that the visual process is a 
genetic growth. In the first, undifferentiated stage of the 
color molecule the Gray process alone exists; later the color 
molecule becomes differentiated so that it is capable of yield- 
ing a pair of antagonistic processes, Y and B ; in a still later 



446 APPENDIX: THE VISUAL PROCESS 

stage the Y component is differentiated so that it furnishes 
two antagonistic processes, R and G; combining the two latter 
processes therefore produces Y, not Gray. Thus the Genetic 
theory meets the most serious difficulty in the Metabolic 
theory. It also reconciles the puzzling phenomena that there 
are four primal colors (5) and only three fundamental colors (4). 

The most serious difficulty in this theory is its inability to 
account satisfactorily for the sensation Black. It also seems 
to assume, like the Metabolic theory, that anabolic processes 
yield nerve impulses and sensations. 

The Genetic theory explains the facts far better than any 
other hypothesis so far devised. One cannot but feel, how- 
ever, that the complex phenomena of visual sensation denote 
a more intricate physiological process than any of the current 
theories presuppose. We have scarcely yet begun to investi- 
gate the fine structural components and elementary chemical 
activities in the retina which play the chief r61e in visual 
stimulation. Till these are better known any hypothesis is 
at best only tentative. 

References 

Helmholtz, H. v., Handbuch der physiologischen Optik, 2d ed. 

Hering, E., Zur Lehre vom Lichtsinne, 1876. 

Hering, E., Grundziige der Lehre vom Lichtsinne, I, IL III; 1905-11 

(Handbuch der Augenheilkunde, 1905, Part I, ch. 12). 
Ladd-Franklin, C, Eine neue Theorie der Lichtempfindungen, Zsch. f. 

Psychol., 1893, 4, 211-221. 
Frankhn, C. L., On Theories of Light-sensation, Mind, N. S., 1893, 2, 473- 

489. 
Parsons, J. H., Introduction to the Study of Colour Vision, Part III. 

(Consult also bibliographical references.) 
Greenwood, M., Physiology of the Special Senses, chs. 17-19. 
Schaefer, E. A., Text-book of Physiology, art. Vision. 
Howell, W. H.. Text-Book of Physiology, ch. 18. 
Kries, J. v., article in Nagel's Handbuch, Vol. III. 
Calkins, M. W., First Book in Psychology, Appendix, sec. III. (Consult 

also bibliographical references.) 
Pillsbury, W. B., Fundamentals of Psychology, ch. 4. 
Titchener, E. B., Text-Book of Psychology, sees. 14-22. 



DIRECTIONS FOR PERFORMING THE EXERCISES 

The practical exercises given at the end of the chapters are 
intended to train the student in precise, critical observation 
of mental phenomena. They may be classed as follows: 

(1) Observation of the student's own experiences; 

(2) Observation of the behavior of others; 

(3) Critical examination of experiences; 

(4) Experiments, requiring exact performance; 

(5) Miscellaneous. 

(1) Self-ohservation. — It is no easy matter to observe and 
report one's own experiences accurately. No one can do this 
successfully without considerable practice. If the problem 
is to examine the nature of your thought of a house, you are 
likely to include not merely the essential factors of the thought 
experience, but various other thoughts and images which the 
word suggests. 

Or again, let the problem be to report what you actually saw 
(perceived) after looking for ten seconds at a certain painting. 
Unless you have trained yourself in observing and reporting 
experiences, your report is almost sure to show important 
omissions, alterations, and actual additions of details. You 
describe a man in the picture as having his eyes open, when 
in point of fact the face is in profile or partly hidden so that 
you saw only one eye. Generally the more common and 
familiar the type of experience, the more liable we are to 
observe carelessly. 

In the exercises which involve observations of your own 
perceptions, thoughts, emotions, etc., what is wanted is an 
exact description of the experience in its proper relations — not 
what you think it probably was, or must have been. You 
should caution yourself again and again to observe carefully, 
and report with precision. Insofar as you fail in either of 



448 DIRECTIONS 

these objectives the value of the report is diminished. At 
the same time it should be remembered that precision in these 
matters can only be attained after considerable practice. 
Accuracy in self-observation is a matter of psychological 
training, not an ethical problem. 

(2) Observation of others. — The same cautions apply to the 
second type of exercises — observation of the behavior of 
other individuals, including children and animals. Unless 
you watch carefully, you are apt to " read into " your obser- 
vation many details which may have occurred but which you 
did not actually observe. In describing the behavior of 
children and animals it is safer to stick to the observed facts and 
avoid assigning motives, 

(3) Analyses. — A third type involves not merely observa- 
tion but critical examination of some personal experience. 
Here the problem is to select the important elements, and to 
indicate so far as possible the order of their importance. 

This involves an additional difficulty. We are inevitably 
influenced by our own presuppositions and by social tradition. 
It requires considerable practice to get rid of these factors. 
You have been told that in states of anger this or that factor 
predominates. But does it, in the specific experience you are 
studying? The aim of this type of exercise is to train you to 
do your own analyzing, instead of depending upon what you 
have been taught, or upon snap judgments, 

(4) Experiments. — In experimental work apparatus has to 
be constructed or prepared. It is important also to arrange 
the entire program with exactness. The details should be 
carefully noted, recorded, and incorporated in the report. In 
an experiment on learning, for instance, the duration of each 
trial and the lapse of time between trials should be decided 
upon in advance. You should note in the record the actual 
duration of work and length of intermissions, as well as the 
amount accomplished and the number of errors. The ex- 
periments given in the book do not call for special apparatus, 



DIREi^x 449 

but they require more or less preparation, and in some cases 
involve the cooperation of a second individual.^ 

General Program. — It is suggested that one exercise be 
undertaken each week, preferably on a topic connected with 
the previous week's study. At least one exercise in each chap- 
ter deals with common, every-day experiences or with famil- 
iar material, and admits of performance at any time. Those 
which deal with unusual phenomena (such as hyperesthesia) 
may be offered as alternatives to students who have had the 
appropriate experiences. 

The reports should be written up in such a way as to be 
easily understood by a " person of average intelligence." 
The description should proceed in consecutive order and 
should be expressed in clear language. Conciseness is pref- 
erable to minute detail, provided nothing essential is omitted. 

The exercises should be performed regularly, week by 
week. If the work is bunched toward the end of the course 
its training value is lost. With school or college classes 
the rule might be made that each exercise be written up and 
handed in on an assigned date. It would be helpful for the 
instructor to discuss with students individually the first 
exercise of each type. 

Bear in mind constantly the two-fold aim of the exercises : 

(1) Accurate observation of the data of psychology and 
their relations. 

(2) Training in scientific method and procedure. 

^ Helpful suggestions regarding procedure will be found in Titchener's 
"Experimental Psychology, Student's Manual"; see especially Introduction 
to Volume 1. 



DIRE<f^^" ""^lONS 



fl 



INDEX 



Absolute pitch, 192 
Accommodation, in learning, 119 

sensations, 242 

visual, 158 
Acquisition, 117 ff. 
Action, rational, eh. xv, 329-331 
Activity, mental; see Conscious ex- 
perience 

neural, app. iii, 435-440; see Im- 
pulse, Nerve impulse 
Adaptation, in behavior, 28, 88 f., 92 
ff., 112 ff., 124 ff., 384, 410 

failures in, 126 

visual, 173 f. 
Adjustment, ch. v, 85-91, 410 

laws, 88 

methods of investigation, 89 ff. 
Affection, affective state, 279 n. ; see 

Feeling 
After-image, 175 n. 
After-sensation, 175 f. 
Ageusia, 220 
All-or-none law, 63 
Anesthesia, 147 

hypnotic, 349 
Anger, 297 
Anosmia, 220 
Anticipation image, 275, 430 

and purpose, 310 f., 427 ff. 
Apperception, 249 ff. 
Appetite, 284 
Appreciation, 369 

Arc, neuro-terminal, 33, 72 ff., 92 ff. 
Aristotle, 136, 339, 437 
Aristotle's experiment, 252 n. 
Association areas, 47 ff. 

fibers, 46 ff. 
Association (of ideas), 139, 339 

classes, 342 f . 

laws, 339 ff. 

rational, 350 ff. 

simultaneous, 142 

successive, 138 ff. 
Associationism, theory of, 334 n. 
Associative memory, 125 f. 



Attainment and capacity, 127 
Attention, 140 f., 364 f. 

fluctuation, 87, 358 

span, 251 
Attitudes, 304, ch. xvii, 360-373 

emotional, 365 ff. 

moral, 370 ff. 

nature and classes, 361 f. 

sentimental, 367 f. 

of thought, 369 f. 
Audition; see Hearing 
Auditory nerve, 190 

qualities, 191 ff. 

receptor, 184 ff. 

sense characters, 191 ff. 

stimuli, 188 ff. 
Automatic control, 312 
Autonomic control, 311 

system, 38, 49 ff. 
Aversion, 284 

Bair, 307 

Baldwin, 387 

Basal ganglia, 45 

Beats, 195 

Behavior, 73 f., 90, chs. vi, vii, 92-132 

and conscious experience, 10 ff. 

instinctive, 102 ff. 

inteUigent, 112 ff. 

reflex, 95 ff. 

types, 94 f., 131 f. 
Behaviorism, 431 n. 
Belief, 304 
Binet, 376 
Binet scale, 378 
Binocular fusion, 247 n. 

parallax, 245 f. 

rivalry, 235 n. 
Black sensation, 167, 175, 181, 442 ff. 
BHndness, 220 f. 

space perception in, 248 n. 
Blind spot, 154 f. 
Border-line experiences, 229 f. 
Brain, 44 ff. 
Bridgman, Laura, 221 



452 



HUMAN PSYCHOLOGY 



Brightness equation, 180 

threshold, 182 f. 
Brovm, Th., 136 

Canals, semicircular, 186 f., 211 f. 
Capacity and attainment, 127 
Cell, characteristics of, 18 ff. 

nerve; see Nerve cell. Neuron 

types, 18, 32, 35 f. 
Central reinforcement, law of, 120 
Central system, role of, 396 
Cerebellum, 45 
Cerebral hemispheres, 46 ff. 
Cerebrospinal system, 38 ff. 
Cerebrum, 46 f. 

Character, human, 360, ch. xviii, 374- 
383 

nature of, 374 f. 

and reputation, 375 n. 
Characters (sensory), auditory, 191 ff. 

of experience, 137 f . 

of feeling, 281 f. 

of sensation, 216 f. 

olfactory, 197 f. 

visual, 163 ff. 
Choice, 308 f., 431 f. 
Chroma, 170 
Chronograph, 356 
Chronoscope, 356 
Circuit, neuro-terminal, 33 
Circulatory sensations, 206 
Clangs, 194 ff. 
Cochlea, 186 ff., 190 
Co-consciousness,. 145 
Coenesthesia, 204 ff. 
Cognition, 270 
Cold Sensation, 201 ff. 
Colligation, 142, 195 
Color hues, 163 ff. 

mixing, 164 

molecule, 181, 445 

shades, 168 ff. 

spindle, 170 ff. 

theory, 180, 441 ff. 

tones, 163 ff. 

zones, 176, 178 
Color blindness, 177 ff., 220 
Colored hearing, 254 f. 
Colors, 163 ff., 441 ff. 

fundamental, 166, 181, 441, 446 

primal, 165 ff., 181, 442, 446 
Combination, mental, 142 
Combination tonps, 194 ff. 



Commissure fibers, 46 f. 
Common end-path, 73 
Communication, 27, 317, 328 
Complementaries, 174, 176, 442 ff. 
Components of mental states, ch. xi, 

215-232 
Comprehension, 320 f. 
Conation, ch. xiii, 286-292 
composition of, 289 f. 
nature of, 286 f. 
role, 292 
varieties, 290 ff. 
and volition, 287 ff. 
Concept, 326 
Conduct, 27, 331, 382 
Conduction, neural, 59 ff., 138, 339 
Cones, retinal, 153 f., 177, 181 
Conscience, 371 f. 

Conscious experience, 10 ff., 91, ch. 
viii, 133-150 
purpose, 427 ff. 
Consciousness, 9 f., 29, 134; see Con- 
scious experience 
and intelligence, 128 f. 
marginal, 87, 146 f. 
subliminal, 145 f. 
Constructive imagination, 275 
Contact sensation, 201 
Contiguity, law of, 340 
Contrast (associative), 339 
Contrast (sensory) , gustatory, 200 vi- \ 

sual, 176 
Control, 311 f., 401 ff. 
of environment, 402 
of perception, 336 
personal, 404 
rational, 328 
of responses, 402 
of self, 403 
social, 403 f. 
of thought, 342 ff. 
Convergence, visual, 160, 245 
Coordination, motor, 85 f. 
Cord, spinal, 38, 43 f. 
Corresponding points in retina', 247 
Cortex, cerebral, 46 ff. 
Corti, organ of, 187 f., 190 
Cranial nerves, 45 f. 
Cubes, illusion of, 262 
Curiosity, 107 f. 
Cutaneous receptors, 201 ff. 
senses, ch. x, 201-204 
space perception, 236 ff. 



INDEX 



453 



Deafness, 220 f. 

Deliberation, 309 

Depth perception, 241 ff. 

Descartes, 136, 413 

Desire, 363 f. 

Determinism, theory of, 431 ff. 

Development, mental, 14, 391, 410 

Dextrality, 108 

Difference, perception of, 257 ff. 

threshold, 258 
Difference tones, 195 f. 
Differentiation, mental, 392 
Digestive sensations, 205 f. 
Direction, perception of, 239 
Directions for practical exercises, 

447 ff. 
Discrimination, 143 ; see Threshold 

perceptual, 257 ff. 
Disorganization, mental, 396 f. 
Dispositions, 365 ff. 
Distance from body, perception of, 

224 n., 241 ff. 
Distance, perception of linear, 236 ff. 
Distant senses, 225 

and purpose, 429 
Distribution of impulses, 68 f., 143 
Double-aspect theory, 134, 149 n., 

415 
Doubt, 304 
Dreams, 229, 344 ff. 
Drugs, effect on consciousness, 147 
Duration character of experience, 

217, 224, 267 
Dynamic sensation, 289 
sentiment, 305 

Ear, structure of, 184 ff. 
Education, role of, 399 
Effectors, 52 ff. 
Effort sensation, 210 
Elimination in learning, 122 
Emotion, ch. xiv, 293-302 

classification, 298 ff. 

nature, 294 

primitive types, 296 ff. 

role, 300 ff. 
End-path, 73 
Environment, 24 f., 402, 409 

and heredity, 399 f. 

role, 397 ff. 
Epicritic sensations, 203 
Epistemology, 417 n. 
Equilibrium sense, 209 I 



Esthetic expression, 108 

sentiment, 304 
Ethics and social psychology, 382 n. 
Evaluative attitude, 369 
Events, perception of, 255 ff. 
Evolution, mental, 28 
Excitation, nervous, 59 ff., 138 
Excitement, mental, 284 
Experience, conscious, 10 ff., 91, 
ch. viii, 133-150; see Conscious- 
ness 

characters, 137 f. 

operations, 138 ff. 

types, 147 ff. 
Experimentation, method in, 448 f. 
Expression, facial, 318 
Expressive states, 286 ff.; see Cona- 
tion 
Extensity character of experience, 

217, 224, 267 
External senses, 222, 225, 233, 417 
Exteroceptors, 222, 225 
Eye movements, 160 

muscles, 156 f. 

physiology, 157 ff. 

structure, 151 ff. 

Facial expression, 318 
Facilitation in learning, 122 
Fallacies of observation, 135 
Familiarity feeUng, 64, 140, 271, 273, 

274 
Fancy, 275 f. 
Fatigue, muscular, 210 

and retention, 438 

sensation, 207 
Fear, 297 

Fechner, 77, 137, 415 
Feeling, 206 f., ch. xiii, 279-286 

characters, 281 f. 

conflicts in, 283 f. 

nature of, 279 ff. 

role, 285 f. 
Fiat, 311 
Fibers, association, 46, 268 

commissure, 46 

nerve, 38 ff. 
Fixation, of habit, 120 ff. 

visual, 160 
Flavor, 200 

Focalization, mental, 140 f. 
Fovea, 155 
Franklin, see Ladd-Franklin 



454 



HUMAN PSYCHOLOGY 



Free image, 274 f. 

nerve endings, 52, 207 
Free-will, 431 ff. 
Frequency, law of, 341 
Freud, 145 f., 301, 348 
Function and structure, 7 n. 

mental, 26 ff. 
Fundamental colors, 166, 442 ff. 
Fusion, binocular, 235, 247 n. 

mental, 142 

neural, 68 

tonal, 194 

Gall, 136 
Ganglia, basal, 45 

spinal, 44 n. 

sympathetic, 49 ff. 
General image, 276 f. 

sensibility, 204, 206 f. 
Genetic visual theory, 181, 445 f. 
Gesture language, 318 
, Glands, 52, 54 f. 
Glandular response, 84 f. 
Goodchild, 17 
Graphic language, 318 ff. 
Gray sensations, 167 f., 442 ff. 
Gustation, see Taste 
Gustatory sense characters, 200 f. 

receptor, 199 

stimuli, 199 

Habit, 27 

conations, 291 

formation, 116 ff. 

and intelligence, 115 f. 
Habits, useful and detrimental, 129 f . 
Hallucinations, 229 f. 
Hartley, 137, £134 n., 339 
Hauser, Kaspar, 398 
Hayes, Lydia P., 248 n. 
Hearing, ch. x, 184-196 

intensity, 196 

physiology of, 190 f. 

qualities, 191 ff. 

sense characters, 191 ff. 

stimuli, 188 ff. 
Heat sensation, 203 
Hedonic law, 282 f. 

quality, 279 f. 

tone, 279 
Helmholtz, 166, 441 
Heredity and environment, 399 f. 
Hering, 166, 443 



Hering illusion, 264 f. 
Herrick, 61 n., 62 n., 435 
Hobbes, 136 
Hues, 163 ff. 

scale of, 165 
Human attitudes, 362, 367, 370 

emotions, 299 

instinctive tendencies, 107 

instincts, 105 

mental states, 231 

reflexes, 101 

temperaments, 376 
Hunger, 205 
Hyperesthesia, 147, 349 
Hypnosis, 349 f. 
Hypnotic suggestion, 349 f. 

Ideals, ch. xv, 329-331 

classification, 330 
Ideas, association of, 139 

laws of succession, 339 ff. 

role, 227 
Ideation, 225 ff. 

criteria, 228 ff. 

and sensation, 147 ff., 216, 228 ff. 
Ideomotor activity, 288, 306 
Illusions of memory, 273 

perceptual, 258 ff. 
Image, anticipation, 275 

free, 274 f. 

general, 276 f. 

imagination, 275 f. 

memory, 271 ff. 

physiology of, 277 f. 

synthetic, 270 
Imageless thought, 322, 440 
Imagery, ch. xiii, 270-279 

laws of selection, 278 

nature and classes, 270 f. 

role, 278 
Imagination, 275 f. 
Imitation, 107, 291 
Immortality, personal, 422 f. 
Impression, 138, 216 n. 
Impulse, 309 n.; see Nervejmgulse 
Indeterminism, theory of, 431 
IndividuaUty, 383 
Inheritance, 399 ff., 409 
Inhibition in learning, 119 f. 

and volition, 309 
Inhibitory impulse, 59 
Instinct, 27 

development of, 109 f. 



INDEX 



455 



evolution of, 103 f. 

human, 104 ff. 

relation to reflex, 102 f. 
Instinctive behavior, ch. vi, 102- 
111 

conation, 291 

control, 312 

tendencies, 107 f. 
Integration, mental, 142 n. 

neural, 86 

spatial, 252 
Intellect, 376 

and intelligence, 376 n. ' 
Intellectual functions, 270 
Intellectuality, 376 ff. 
Intelligence, ch. vii, 112-132 

and adjustment, 130 f. 

classification, 130 

and consciousness, 128 f. 

growth of, 126 ff. 

and habit, 115 f. 

and intellect, 376 n. 

nature of, 112 ff. 

neural basis, 115 

significance of, 128 ff. 
IntelUgent behavior, see Intelligence 
Intensity, 77 f. ; see Weber's Law 

of experience, 137 f. 

of feeUng, 282 f. 

of idea, 228 

of nerve impulse, 56 ff. 

of sensation, 181 ff., 196, 198 f., 
200 f., 204, 210 f., 213, 217 
Interaction theory, 414 
Interest, 362 f. 
Internuncial paths, 47 
Interoceptors, 223, 225 
Interpretive attitude, 369 
Intervals, musical, 192 f. 
Introspection, 11, 416; see Self-ob- 
servation 
Itching sensation, 204 

James, 105, 295, 334, 419 
Janet, 386 
Judgment, 326 f. 

Keller, Helen, 221, 376, 398 
Kinesthetic senses, ch. x, 209-211 

qualities, 210 

stimuli, 209 
Knowledge, problem of, 417 n. 
KrauBC corpuscle, 202 f. 



Labyrinth, 186 f. 
Ladd-Franklin, 181, 445 
Lange, 295 
Langley, 183 
Language, ch. xv, 314-329 

role, 328 f. 

social origin, 316 f. 

types, 317 
Learning, 116 ff. 

curve of, 124 
Least perceptible brightness, 182 f. 

see Threshold 
Limen; see Threshold 
Local sign, 219 f., 236 ff. 
Locomotion, 27, 106, 114 n. 
Love, 297 
Luciani, 62 n. 

Marginal consciousness, 87, 146 f. 
Masson disk, 182 
Mazes, 113 
McDougall, 298 
Meaning, 323 ff. 

judgment, 327 

in reasoning, 352 
Mechanism, neuro-terminal, 32 ff. 
Mechanism (theory of), 425 

psychological, 429 

and purpose, app. ii, 425-434 
Medulla, 45 

Meissner corpuscle, 202 f. 
Memory, associative, 125 f. 

in dreams, 347 

factors, 272 f. 

illusions, 273 f. 

images, 271 ff. 

revival, 140 
Mental, see Mental states. Experi- 
ence 

chemistry, 143 n. 

and conscious, 10 n. 

development, ch. xix, 391-404 

functions, 26 ff. 

synthesis, 143 n. 

tests, 378 f., 380 f. 
Mental life, 7 ft. 

evolution of, 28 
structural basis, 32 ff. 
Mental organization, 24 ff., 392 ff. 
factors in, 394 ff. 
types, 400 f. 
Mental states, chs. xii-xv, 233-333 
classes of, 230 ff. 



456 



HUMAN PSYCHOLOGY 



primary, chs. xii, xiii, 233-292 
secondary, chs. xiv, xv, 293-333 
succession of, ch. xvi, 334-359 
summary, 331 ff. 

Mentality and vitality, 7 S. 

Metabolic variation, neural, 66 f., 140 

Metabolic visual theories, 443 ff. 

Metabolism, in cell, 20 
neural, 66 f., 437 ff. 

Meyer pattern, 176 

Mill, J., 137, 339 

Mind; see Consciousness, Mentality, 
Mental states 

Mind-body relation, app. i, 413-425 

Mirror-pictures, 265 f. 

Mirror-writing, 121 n., 266, 319 

Misprints, 262 

Mitosis of cell, 20 

Mnemonic combination, 125 f. 

Mode of nerve impulse, 58, 75 ff., 82, 
435 S. 

Modification, neural, 69 f., 437 ff. 

Mood, 367 

Moral attitudes, 371 f. 
sentiments, 305 

Morality, 381 ff. 

Morgan, LI., 63 

Motives, 330, 365 

Motor consciousness, 287; see Cona- 
tion 
nerves, 41 f. 
senses, 209, 222 f. 

Movement; see Conation, Volition, 
Kinesthetic senses 

Miiller-Lyer illusion, 264 f. 

Muscle sense; see Kinesthetic senses 

Muscles, 52 ff. 

Musical intervals, 192 f. 

Nausea, 205 

Nerve, properties of, 144 
Nerve cell, types, 35 f.; see Neuron 
Nerve impulse, 52 n., 56 ff. 
mode of, 58 f. 
nature of, 435 ff. 
Nerve substance, operations of, 59 ff. 
Nerves, 39 ff. 
cranial, 41, 45 f. 
sensory and motor, 39 ff. 
spinal, 41 
Nervous arc, 72 ff. 

operation of, 92 ff. 

operation of segments, ch. v, 73-9 1 



Nervous system, ch. iii, 34-51; see 
Neuro-terminal mechanism 
central, 38, 43 ff. 
physiology of, 56 ff. 

Neural activity, app. iii, 435-440 

Neuron, physiology of, ch. iv, 56-71 
structure of, 34 ff. 

Neuro-terminal circuit, 33 
mechanism, ch. iii, 32-55, 409 

Newton, 4, 166 

Noise, 191, 196 

Object perception, 251 ff. 
Objective and subjective phenomena, 

134, 413 ff. 
Observation, self; see Self -observa- 
tion 

scientific, 134 ff. 
Odors, classes of, 197 f. 
Olfaction, see Smell 
Olfactometer, 198 
Olfactory receptor, 196 f. 

stimuli, 197 
Operations of nervous are, 78 f. 

of conscious experience, 138 ff. 
Optic nerve, 158 f. 
Organs, effector, 52 ff; 

receptor, 51 ff.; see Receptors 

terminal, 51 ff. 
Organic senses, ch. x, 204-207 
Organism, ch. ii, 17-31 

chemistry of, 17 ff. 

and organization, 392 n. 
Organization, 6 f., 17 ff; 

mental, 24 ff. 

psychobiological, 28 f. 

and organism, 392 n. 
Organized mental life, ch. xix, 391— 

404 
Overtones, 194 

Pacinian corpuscle, 202 f. 

Pain sense, 201, 204, ch. x, 207-208 

qualities, 207 f. 
Parallax, binocular, 245 f. 
Parallelism, theory of, 414 
Perception, ch. xii, 233-269 

of depth, 241 ff. 

of differences, 257 ff. 

of events, 255 ff. . 

of external world, 416 ff. 

focused, 249 ff. 

illusions of, 258 ff. 



INDEX 



457 



mechanism of, 239 

nature of, 233 f. 

of objects, 251 if. 

physiology of, 267 f. 

relation to sensation, 266 f. 

simple, 234 f. 

stream of, 335 ff. 

superficial, 235 ff. 

of time and rhythm, 255 ff. 
Perceptual succession, laws of, 337 f. 
Perimeter, 176 f. 
Peripheral vision, 176 f., 442 ff. 
Periphery of retina, 155 f. 
Permanent mental conditions, chs. 

xvii, xviii, 360-390 
Perry, 429 
Personal control, 404 

identity, 385 
Personality, 361, ch. xviii, 383-388, 
404 

multiple, 385 ff. 
Personification of nature, 433 f. 
Perspective, visual, 243, 260 ff. 

temporal, 274 
Phonography, 319 
Phrenology, 136 
Physiology of conation, 286 

of emotion, 295 

of feeling, 281 

of imagery, 277 f. 

neural, ch. iv, 56-71 

of perception, 267 f. 

of sensation, 157 ff., 190 f., 197, 
199 

of volition, 309 
Pitch, 191 ff. 

absolute, 192 

relative, 192 

standard, 192 
Play, 108 

Pleasantness, 206, 280 ff., 300 
Pons Varolii, 45 
Present, perceptual, 255 
Pressure sensation, 201 
Priestley, 136 

Primal colors, 165 ff., 442 ff. 
Primary mental states, chs. xii, xiii, 

233-292 
Problem attitude, 369 
Projection areas, 47 f. 
Projection (mental), 241 ff. 
central processes in, 246 f. 
law of, 249 



tactile, 248 f. 

visual, 241 ff. 
Properties of experience, 137 n. 

of nerve, 144 
Proposition, 327 
Proprioceptors, 223, 225 
Protopathic sensations, 203 
Psychical research, 418 ff. 
Psychological mechanism, theory of, 

429 
Psychology, abnormal, 15 

applied, 2, 383 n. 

branches, 13 ff. 

definition, 1, 13 

descriptive, 14 f. 

experimental, 16 

genetic, 3, 14 

individual, 384 

physiological, 15 

race, 16 

relation to biology, 5 f. 

religious, 16 

science of, ch. i, 1-16 

social, 6, 382 n. 
Psychophysical parallelism, theory 

of, 414 
Psychophysics, 16 

Purkinje phenomenon, 173, 182, 442 ff. 
Purpose, 310 f. 

conscious, 427 ff. 

in organic growth, 425 ff. 
Puzzle pictures, 262 ff. 

Qualities of sensation, 163 ff., 170; 
180 f., 191 ff., 197 f., 200, 203 f., 
205 ff., 207 f., 210 f., 212 f. 

Rational action, 27, ch. xv, 329-331 

control, 328 

expression, 327, 328 

thinking, 350 ff. 

thought, 326 f. 
Reaction, see Response 
Reaction time, 356 f. 
Reading, 320 f. 

aloud, 321 n. 
ReaUty feeling, 303 f. 
Reasoning, 350 ff . ; see Rational ac- 
tion, etc. 
Recall, 272 
Recency, law of, 341 
Receptors, 51 f., 151 ff., 184 ff., 196, 
199, 201, 211 



458 



HUMAN PSYCHOLOGY 



classes, 222 f. 

defective, 220 

role in stimulation, 78 ff. 

and sensation, 218 ff. 
Reflex behavior, ch. vi, 95-101 

conation, 290 f. 
Reflexes, 95 ff. 

human, 100 f. 

nature of, 99 f. 

ocular, 158 ff. 

spinal, 73 
Refractory period, 61 
Reinstatement, law of, 341 
Reputation and character, 375 n. 
Response, ch. v, 81-85 

control of, 402 

factors determining, 82 ff. 

general laws, 84 f. 

glandular, 84 f. 

muscular, 81 ff. 
Respiratory sensations, 206 
Responsibility, 431 ff. 
Retention, 63 ff., 140, 272 

nature of, 437 ff. 

permanency, 65 

and purpose, 429 
Retina, 153 ff. 

corresponding points in, 247 
Revival, 140 

Rhythm, perception of, 255 ff. 
Right-handedness, 108 
Rivalry, binocular, 235 n. 
Rods, retinal, 154, 177 
Rolandic fissure, 47 f. 

Satisfaction, 364 
Saturation, 170 
Scale, musical, 192 f. 
Science, art, and genetics, 1 ff. 

classification, 3 ff. 
Secondary mental states, chs. xiv, 
XV, 293-333 

classification, 294 

nature of, 293 f. 
Self, 383 ff., see Personality 
Self-consciousness, 387 f. 
Self-control, 403 
Self-notion, 387 f. 
Self-observation, 9 ff., 133 ff., 447 
Selkirk, Alexander, 398 
Semicircular canals, 186 f., 211 f. 
Sensation, 77; see Senses 

characters", 216 f. 



classes, 221 ff. 
criteria of, 228 ff. 
and ideation, 147 ff., 216, 228 ff. 
number of, 223 f. 
Sense organs, see Reeeptors 
Senses, 149, ch. ix, x, 151-214 
classification of, 221 ff., 225 
Sensorimotor activity, 288 
Sensory characters, law of, 224 
nerves, 41 ff. 

neurons, role in reception, 80 
Sentiment, ch. xiv, 302-306 
classification, 302 f. 
nature, 302 
role, 305 
Sentimental attitudes, 367 f. 
Set, neural, 63 
Sexual sensations, 206 
Shades, 167 f. 

of color, 168 f. 
Sight, ch. ix, 151-183, 441 ff, 
intensity, 181 ff. 
qualities, 163 ff. 
receptor, 151 ff. 

space perception in, 237 ff., 241 f?. 
stimulus, 160 ff. 
theory of, 180 f., 441 ff. 
Similarity, law of, 339 
Simon, 376 
Simple perception, 234 f. 

response, 27 
Skill, 379 ff. 
Sleep, 344 ff. 
Smell, ch. x, 196-198 
Social control, 403 f. 
environment, 398 f. 
psychology and ethics, 382 n. 
Somnambulism, 345 
Sound waves, 188 ff. 
Space location in memory, 272 
Space perception, 235 ff. 

of blind, 248 n. 
Span of attention, 251 
Specific nerve energy, 59 
Speech, 318 
Spinal circuit, 73 
cord, 38, 43 f. 
Spurzheim, 136 
Staircase illusion, 261 
States, mental, see Mental states • 
Static receptor, 211 f. 

sense, 209, ch. x, 211-213 
Stereoscope, 246, 418 



INDEX 



459 



Stimulation, ch. v, 74-81 

general laws, 80 f. 

role of receptor, 78 ff. 

role of stimulus, 75 
Stimulus, 75 ff. 

auditory, 188 ff. 

gustatory, 199 

inadequate, 76 

kinesthetic, 209 

olfactory, 197 

organic, 206 

role of, 75, 397 f. 

and sensation, 217 f. 

static, 213 

visual, 160 ff. 
Strain sensation, 210 
Stratton's experiment, 252 f. 
Stream of consciousness, 334 

of experiences, 354 f. 

of perception, 335 ff. 

of thought, 338 
Structure and function, 7 n. 
Subconscious experience, 144 f. 
Subconsciousness, 144 ff. 
Subjective experience, 215 

and objective phenomena, 134, 
413 ff. 
Sublime, sentiment of, 305 
Subliminal consciousness, 145 f. 
Succession of mental states, ch. xvi, 
334-359 

law of, 357 f. 
Suggestion, 138 ff., 339 ff. 

hypnotic, 349 f. 
Sully, 385 

Summary, general, 405 ff. 
Summation of impulses, 67 f., 142 
Surface perception, 235 ff. 
SjTnbolic mental states, 314 f. 
Sympathetic ganglia, 49 ff. 

system, 38 
Sympathy, 298 
Synapses, 37 f., 437 

and learning, 117 ff. 
Synesthesia, 254 f. 
Systemic senses, 204 ff., 222 f. 

Tactile, see Touch 

space i)erception, 236 ff. 
Taste, ch. x, 199-201 
Telekinesis, 418, 421 f. 
Telepathy, 418 
Temperament, 375 f. 



Temperature senses, 201 ff. 
Temporal location in memory, 272 f. 

perspective, 274 
Tendencies, instinctive, 107 f. 
Tendential conations, 291 
Terminal organs, ch. iii, 51-55; see 
Effectors, Receptors 
role of, 395 f. 
Terms, 327 

Tests, mental, 378 f., 380 f. 
Thinking, 350 n. 
Thorndike, 106 

Thought, 277, ch. xv, 314-329 
control of, 342 ff. 
imageless, 32* f., 440 
nature and types, 320 ff. 
role, 328 f. 
stream of, 338 
Thought-transference, 418 ff. 
Three-color visual theories, 441 ff. 
Threshold, 182, 196, 198, 201, 204, 
211, 213 
of difference, 183, 258 f. 
Tickle sensation, 204 
Timbre, 194 
Time perception, 255 ff. 
Tingling sensation, 204 
Tint, 168 ff. 

Titchener, 208, 255, 357, 415, 449 n. 
Tone-deafness, 220 
Tones, 191 ff. 
Touch, 201 ff. 
qualities, 203 f. 
space perception in, 236 ff. 
Trace, neural, 63 

Transformation, mental, 143 f., 323 
Trial and error, 125, 312 
Tunes, 256 
Tweney, 17 

Twilight vision, 177, 182 
Types, mental, 400 f. 

Understanding, 320 n. 
Unpleasantness, 206, 279 ff., 300 

Value, 302, 324 ff. 

judgment, 327 

in reasoning, 352 
Vater-Pacini corpuscle, 202 f. 
Visceral senses, 204 ff. 
Vision, see Sight 
Visual intensity, 181 ff. 

process, app. iv, 441-446 



460 



HUMAN PSYCHOLOGY 



qualities, 163 ff. 

receptor, 151 ff. 

sense characters, 163 ff. 

space perception, 237 ff., 241 ff. 

stimulus, 160 ff. 

theory, 180 f., 441 ff. 
Vital functions, 22 f . 
Vitalism, theory of, 425 
Vividness, 140 f. 

law of, 341 
Vocal language, 318 
Volition, ch. xiv, 306-313 

and conation, 387 ff. 

and inhibition, 309 

nature, 306 ff. « 

role, 313 



Voluntarism, theory of, 428 
Voluntary activity, 308 ff. 
control, 311 f. 

Walking, 106, 114 

Want, 364 

Warmth sensation, 201 ff. 

Weber, 77, 137, 217, 238 

Weber's Law, 78, 217, 219, 258 f., 282 

Will, 307; see Volition 

Writing, 318 ff. 

Wundt, 137, 282 

Yellow sensation, 181, 445 f. 
Young, 166, 441 



IRB S 76 



